diff --git a/.editorconfig b/.editorconfig
index 59b337b6..009c31a3 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -1,27 +1,27 @@
-# top-most EditorConfig file
-root = true
-
-# All PHP files MUST use the Unix LF (linefeed) line ending.
-# Code MUST use an indent of 4 spaces, and MUST NOT use tabs for indenting.
-# All PHP files MUST end with a single blank line.
-# There MUST NOT be trailing whitespace at the end of non-blank lines.
-[*]
-charset = utf-8
-end_of_line = crlf
-insert_final_newline = true
-trim_trailing_whitespace = true
-
-# PHP-Files, Composer.json, MD-Files
-[{*.php,composer.json,*.md}]
-indent_style = space
-indent_size = 4
-
-# HTML-Files LESS-Files SASS-Files CSS-Files JS-Files JSON-Files
-[{*.html,*.less,*.sass,*.css,*.js,*.json}]
-indent_style = tab
-indent_size = 4
-
-# Gitlab-CI, Travis-CI
-[*.yml]
-indent_style = space
-indent_size = 2
\ No newline at end of file
+# top-most EditorConfig file
+root = true
+
+# All PHP files MUST use the Unix LF (linefeed) line ending.
+# Code MUST use an indent of 4 spaces, and MUST NOT use tabs for indenting.
+# All PHP files MUST end with a single blank line.
+# There MUST NOT be trailing whitespace at the end of non-blank lines.
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+# PHP-Files, Composer.json, MD-Files
+[{*.php,composer.json,*.md}]
+indent_style = space
+indent_size = 4
+
+# HTML-Files LESS-Files SASS-Files CSS-Files JS-Files JSON-Files
+[{*.html,*.less,*.sass,*.css,*.js,*.json}]
+indent_style = tab
+indent_size = 4
+
+# Gitlab-CI, Travis-CI
+[*.yml]
+indent_style = space
+indent_size = 2
diff --git a/composer.json b/composer.json
index f0d91a52..677c45e9 100644
--- a/composer.json
+++ b/composer.json
@@ -1,35 +1,38 @@
-{
-	"name": "microsoft/microsoft-graph-core",
-	"type": "library",
-	"description": "The Microsoft Graph SDK for PHP",
-	"homepage": "https://developer.microsoft.com/en-us/graph",
-	"license": "MIT",
-	"authors": [
-		{
-			"name": "Microsoft Graph Client Tooling",
-			"email": "graphtooling@service.microsoft.com",
-			"role": "Developer"
-		}
-	],
-	"require": {
-		"php": "^8.0 || ^7.3",
-		"guzzlehttp/guzzle": "^6.0 || ^7.0",
-		"ext-json": "*"
-	},
-	"require-dev": {
-		"phpunit/phpunit": "^8.0 || ^9.0",
-		"mikey179/vfsstream": "^1.2",
-		"phpstan/phpstan": "^0.12.90"
-	},
-	"autoload": {
-		"psr-4": {
-			"Microsoft\\Graph\\": "src/"
-		}
-	},
-	"autoload-dev": {
-		"psr-4": {
-			"Microsoft\\Graph\\Test\\": "tests/",
-			"Microsoft\\Graph\\Http\\Test\\": "tests/Http/"
-		}
-	}
-}
+{
+	"name": "microsoft/microsoft-graph-core",
+	"type": "library",
+	"description": "The Microsoft Graph SDK for PHP",
+	"homepage": "https://developer.microsoft.com/en-us/graph",
+	"license": "MIT",
+	"authors": [
+		{
+			"name": "Microsoft Graph Client Tooling",
+			"email": "graphtooling@service.microsoft.com",
+			"role": "Developer"
+		}
+	],
+	"require": {
+		"php": "^8.0 || ^7.3",
+		"guzzlehttp/guzzle": "^7.0",
+		"guzzlehttp/psr7": "^2.0",
+		"php-http/httplug": "^2.2",
+		"php-http/guzzle7-adapter": "^1.0",
+		"ext-json": "*"
+	},
+	"require-dev": {
+		"phpunit/phpunit": "^8.0 || ^9.0",
+		"mikey179/vfsstream": "^1.2",
+		"phpstan/phpstan": "^0.12.90"
+	},
+	"autoload": {
+		"psr-4": {
+			"Microsoft\\Graph\\": "src/"
+		}
+	},
+	"autoload-dev": {
+		"psr-4": {
+			"Microsoft\\Graph\\Test\\": "tests/",
+			"Microsoft\\Graph\\Http\\Test\\": "tests/Http/"
+		}
+	}
+}
\ No newline at end of file
diff --git a/src/Core/Enum.php b/src/Core/Enum.php
index 6ff3f6b1..803d4990 100644
--- a/src/Core/Enum.php
+++ b/src/Core/Enum.php
@@ -101,4 +101,4 @@ public function value()
     {
         return $this->_value;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Core/ExceptionWrapper.php b/src/Core/ExceptionWrapper.php
deleted file mode 100644
index 574b79dc..00000000
--- a/src/Core/ExceptionWrapper.php
+++ /dev/null
@@ -1,77 +0,0 @@
-<?php
-/**
-* Copyright (c) Microsoft Corporation.  All Rights Reserved.
-* Licensed under the MIT License.  See License in the project root
-* for license information.
-*
-* ExceptionWrapper File
-* PHP version 7
-*
-* @category  Library
-* @package   Microsoft.Graph
-* @copyright 2016 Microsoft Corporation
-* @license   https://opensource.org/licenses/MIT MIT License
-* @version   GIT: 0.1.0
-* @link      https://graph.microsoft.io/
-*/
-
-namespace Microsoft\Graph\Core;
-
-use GuzzleHttp\Exception\BadResponseException;
-
-/**
- * Class ExceptionWrapper
- *
- * @category Library
- * @package  Microsoft.Graph
- * @license  https://opensource.org/licenses/MIT MIT License
- * @link     https://graph.microsoft.io/
- */
-class ExceptionWrapper
-{
-    /**
-     * Wrap Guzzle BadResponseException which returns truncated exception messages for 4xx and 5xx responses.
-     * Adds response body to the exception message.
-     *
-     * @param BadResponseException $ex
-     * @return BadResponseException containing HTTP response from Graph API
-     */
-    public static function wrapGuzzleBadResponseException(BadResponseException $ex)
-    {
-        $response = $ex->getResponse();
-
-        // Safety check for Guzzle < 7.0
-        if (!$response) {
-            return $ex;
-        }
-
-        /** @see \GuzzleHttp\Exception\RequestException::create() */
-        if (preg_match('/^(.+: `.+ .+` resulted in a `.+ .+` response):\n/U', $ex->getMessage(), $match)) {
-            $message = $match[1];
-
-            $body = $response->getBody();
-
-            if (!$body->isSeekable() || !$body->isReadable()) {
-                return $ex;
-            }
-
-            $summary = $body->getContents();
-            $body->rewind();
-
-            if ($summary !== '') {
-                $message .= ":\n{$summary}\n";
-
-                //return new $ex($message, $ex->getRequest(), $ex->getResponse(), $ex, $ex->getHandlerContext());
-                // Better: modify internal message inside original exception object (preserves the stack trace)
-                (new class() extends \Exception {
-                    public static function overwriteProtectedMessage(\Exception $ex, $message)
-                    {
-                        $ex->message = $message;
-                    }
-                })::overwriteProtectedMessage($ex, $message);
-            }
-        }
-
-        return $ex;
-    }
-}
diff --git a/src/Core/GraphConstants.php b/src/Core/GraphConstants.php
index a92eb77c..39a79cdb 100644
--- a/src/Core/GraphConstants.php
+++ b/src/Core/GraphConstants.php
@@ -19,7 +19,6 @@
 final class GraphConstants
 {
     // These can be overwritten in setters in the Graph object
-    const API_VERSION = "v1.0";
     const REST_ENDPOINT = "https://graph.microsoft.com/";
 
     // Define HTTP request constants
diff --git a/src/Core/NationalCloud.php b/src/Core/NationalCloud.php
new file mode 100644
index 00000000..e863d5da
--- /dev/null
+++ b/src/Core/NationalCloud.php
@@ -0,0 +1,65 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ */
+
+namespace Microsoft\Graph\Core;
+
+/**
+ * Class NationalCloud
+ *
+ * Defines Graph hosts for the various national clouds
+ *
+ * @package Microsoft\Graph\Core
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
+ */
+final class NationalCloud
+{
+    const GLOBAL = "https://graph.microsoft.com";
+    const US_GOV = "https://graph.microsoft.us";
+    const US_DOD = "https://dod-graph.microsoft.us";
+    const GERMANY = "https://graph.microsoft.de";
+    const CHINA = "https://microsoftgraph.chinacloudapi.cn";
+
+    /**
+     * Unique hostnames from constant values [graph.microsoft.com, graph.microsoft.us, ...]
+     *
+     * @var array
+     */
+    private static $hosts = [];
+
+    /**
+     * Checks if url contains a valid National Cloud host
+     *
+     * @param string $url
+     * @return bool
+     */
+    public static function containsNationalCloudHost(string $url): bool {
+        self::initHosts();
+        $validUrlParts = parse_url($url);
+        return $validUrlParts
+                && array_key_exists("scheme", $validUrlParts)
+                && $validUrlParts["scheme"] == "https"
+                && array_key_exists("host", $validUrlParts)
+                && array_key_exists(strtolower($validUrlParts["host"]), self::$hosts);
+    }
+
+    /**
+     * Extracts hostnames from constant values to an array with unique keys for optimal lookup
+     */
+    private static function initHosts(): void {
+        if (!self::$hosts) {
+            $reflectedClass = new \ReflectionClass(__CLASS__);
+            $constants = $reflectedClass->getConstants();
+            foreach ($constants as $constName => $url) {
+                // Create associative array for O(1) key lookup
+                $hostname = parse_url($url)["host"];
+                self::$hosts[$hostname] = true;
+            }
+        }
+    }
+}
diff --git a/src/Exception/GraphClientException.php b/src/Exception/GraphClientException.php
new file mode 100644
index 00000000..d944d391
--- /dev/null
+++ b/src/Exception/GraphClientException.php
@@ -0,0 +1,21 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ */
+
+namespace Microsoft\Graph\Exception;
+
+/**
+ * Class ClientInitialisationException
+ *
+ * @package Microsoft\Graph\Exception
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
+ */
+class GraphClientException extends GraphException
+{
+
+}
diff --git a/src/Exception/GraphException.php b/src/Exception/GraphException.php
index 0c402ab7..61e1ce49 100644
--- a/src/Exception/GraphException.php
+++ b/src/Exception/GraphException.php
@@ -1,9 +1,9 @@
-<?php 
+<?php
 /**
-* Copyright (c) Microsoft Corporation.  All Rights Reserved.  
-* Licensed under the MIT License.  See License in the project root 
+* Copyright (c) Microsoft Corporation.  All Rights Reserved.
+* Licensed under the MIT License.  See License in the project root
 * for license information.
-* 
+*
 * Exceptions File
 * PHP version 7
 *
@@ -46,6 +46,6 @@ public function __construct($message, $code = 0, $previous = null)
     */
     public function __toString()
     {
-        return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
+        return get_called_class() . ": [{$this->code}]: {$this->message}\n";
     }
-}
\ No newline at end of file
+}
diff --git a/src/Graph.php b/src/Graph.php
deleted file mode 100644
index f32dc7c9..00000000
--- a/src/Graph.php
+++ /dev/null
@@ -1,184 +0,0 @@
-<?php
-/**
-* Copyright (c) Microsoft Corporation.  All Rights Reserved.
-* Licensed under the MIT License.  See License in the project root
-* for license information.
-*
-* Graph File
-* PHP version 7
-*
-* @category  Library
-* @package   Microsoft.Graph
-* @copyright 2016 Microsoft Corporation
-* @license   https://opensource.org/licenses/MIT MIT License
-* @version   GIT: 0.1.0
-* @link      https://graph.microsoft.io/
-*/
-
-namespace Microsoft\Graph;
-
-use Microsoft\Graph\Core\GraphConstants;
-use Microsoft\Graph\Http\GraphCollectionRequest;
-use Microsoft\Graph\Http\GraphRequest;
-
-/**
- * Class Graph
- *
- * @category Library
- * @package  Microsoft.Graph
- * @license  https://opensource.org/licenses/MIT MIT License
- * @link     https://graph.microsoft.io/
- */
-class Graph
-{
-    /**
-    * The access_token provided after authenticating
-    * with Microsoft Graph (required)
-    *
-    * @var string
-    */
-    private $_accessToken;
-    /**
-    * The api version to use ("v1.0", "beta")
-    * Default is "v1.0"
-    *
-    * @var string
-    */
-    private $_apiVersion;
-    /**
-    * The base url to call
-    * Default is "https://graph.microsoft.com"
-    *
-    * @var string
-    */
-    private $_baseUrl;
-    /**
-    * The port to use for proxy requests
-    * Null disables port forwarding
-    *
-    * @var string
-    */
-    private $_proxyPort;
-
-    /**
-     * Whether SSL verification should be used for proxy requests
-     *
-     * @var bool
-     */
-    private $_proxyVerifySSL;
-
-    /**
-    * Creates a new Graph object, which is used to call the Graph API
-    */
-    public function __construct()
-    {
-        $this->_apiVersion = GraphConstants::API_VERSION;
-        $this->_baseUrl = GraphConstants::REST_ENDPOINT;
-    }
-
-    /**
-    * Sets the Base URL to call (defaults to https://graph.microsoft.com)
-    *
-    * @param string $baseUrl The URL to call
-    *
-    * @return Graph object
-    */
-    public function setBaseUrl($baseUrl)
-    {
-        $this->_baseUrl = $baseUrl;
-        return $this;
-    }
-
-    /**
-    * Sets the API version to use, e.g. "beta" (defaults to v1.0)
-    *
-    * @param string $apiVersion The API version to use
-    *
-    * @return Graph object
-    */
-    public function setApiVersion($apiVersion)
-    {
-        $this->_apiVersion = $apiVersion;
-        return $this;
-    }
-
-    /**
-    * Sets the access token. A valid access token is required
-    * to run queries against Graph
-    *
-    * @param string $accessToken The user's access token, retrieved from
-    *                     MS auth
-    *
-    * @return Graph object
-    */
-    public function setAccessToken($accessToken)
-    {
-        $this->_accessToken = $accessToken;
-        return $this;
-    }
-
-    /**
-    * Sets the proxy port. This allows you
-    * to use tools such as Fiddler to view
-    * requests and responses made with Guzzle
-    *
-    * @param string $port The port number to use
-    * @param bool $verifySSL Whether SSL verification should be enabled
-    *
-    * @return Graph object
-    */
-    public function setProxyPort($port, $verifySSL = false)
-    {
-        $this->_proxyPort = $port;
-        $this->_proxyVerifySSL = $verifySSL;
-
-        return $this;
-    }
-
-	/**
-	 * Creates a new request object with the given Graph information
-	 *
-	 * @param string $requestType The HTTP method to use, e.g. "GET" or "POST"
-	 * @param string $endpoint    The Graph endpoint to call
-	 *
-	 * @return GraphRequest The request object, which can be used to
-	 *                      make queries against Graph
-	 * @throws Exception\GraphException
-	 */
-    public function createRequest($requestType, $endpoint)
-    {
-        return new GraphRequest(
-            $requestType,
-            $endpoint,
-            $this->_accessToken,
-            $this->_baseUrl,
-            $this->_apiVersion,
-            $this->_proxyPort,
-            $this->_proxyVerifySSL
-        );
-    }
-
-	/**
-	 * Creates a new collection request object with the given
-	 * Graph information
-	 *
-	 * @param string $requestType The HTTP method to use, e.g. "GET" or "POST"
-	 * @param string $endpoint    The Graph endpoint to call
-	 *
-	 * @return GraphCollectionRequest The request object, which can be
-	 *                                used to make queries against Graph
-	 * @throws Exception\GraphException
-	 */
-    public function createCollectionRequest($requestType, $endpoint)
-    {
-        return new GraphCollectionRequest(
-            $requestType,
-            $endpoint,
-            $this->_accessToken,
-            $this->_baseUrl,
-            $this->_apiVersion,
-            $this->_proxyPort,
-            $this->_proxyVerifySSL
-        );
-    }
-}
diff --git a/src/Http/AbstractGraphClient.php b/src/Http/AbstractGraphClient.php
new file mode 100644
index 00000000..20ab94a9
--- /dev/null
+++ b/src/Http/AbstractGraphClient.php
@@ -0,0 +1,154 @@
+<?php
+/**
+* Copyright (c) Microsoft Corporation.  All Rights Reserved.
+* Licensed under the MIT License.  See License in the project root
+* for license information.
+*/
+
+namespace Microsoft\Graph\Http;
+
+use Microsoft\Graph\Core\GraphConstants;
+use Microsoft\Graph\Core\NationalCloud;
+use Microsoft\Graph\Exception\GraphClientException;
+use Microsoft\Graph\Exception\GraphException;
+
+/**
+ * Class BaseClient
+ *
+ * Base class to be extended by Graph client classes in v1 and beta packages
+ *
+ * @package Microsoft\Graph
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
+ */
+abstract class AbstractGraphClient
+{
+    /**
+    * The access_token provided after authenticating
+    * with Microsoft Graph (required)
+    *
+    * @var string
+    */
+    private $accessToken;
+
+    /**
+     * Host to use as the base URL and for authentication
+     * @var string
+     */
+    private $nationalCloud = NationalCloud::GLOBAL;
+
+    /**
+     * HttpClient to use for requests
+     * @var HttpClientInterface
+     */
+    private $httpClient = null;
+
+
+    /**
+     * BaseClient constructor.
+     *
+     * Creates a Graph client object used to make requests to the Graph API
+     *
+     * @param string|null $nationalCloud if null defaults to "https://graph.microsoft.com"
+     * @param HttpClientInterface|null $httpClient if null creates default Guzzle client
+     * @throws GraphClientException
+     */
+    public function __construct(?string $nationalCloud = NationalCloud::GLOBAL,
+                                ?HttpClientInterface  $httpClient = null)
+    {
+        $this->nationalCloud = ($nationalCloud) ?: NationalCloud::GLOBAL;
+        $this->httpClient = ($httpClient) ?: HttpClientFactory::nationalCloud($nationalCloud)::createAdapter();
+    }
+
+    /**
+    * Sets the access token. A valid access token is required
+    * to run queries against Graph
+    *
+    * @param string $accessToken The user's access token, retrieved from
+    *                     MS auth
+    *
+    * @return $this object
+    */
+    public function setAccessToken(string $accessToken): self
+    {
+        $this->accessToken = $accessToken;
+        return $this;
+    }
+
+    /**
+     * @return string
+     */
+    public function getAccessToken(): string {
+        return $this->accessToken;
+    }
+
+    /**
+     * @return string
+     */
+    public function getNationalCloud(): string
+    {
+        return $this->nationalCloud;
+    }
+
+    /**
+     * @return HttpClientInterface
+     */
+    public function getHttpClient(): HttpClientInterface
+    {
+        return $this->httpClient;
+    }
+
+	/**
+	 * Creates a new request object with the given Graph information
+	 *
+	 * @param string $requestType The HTTP method to use, e.g. "GET" or "POST"
+	 * @param string $endpoint    The Graph endpoint to call
+	 *
+	 * @return GraphRequest The request object, which can be used to
+	 *                      make queries against Graph
+	 * @throws GraphException
+	 */
+    public function createRequest(string $requestType, string $endpoint): GraphRequest
+    {
+        return new GraphRequest(
+            $requestType,
+            $endpoint,
+            $this
+        );
+    }
+
+	/**
+	 * Creates a new collection request object with the given
+	 * Graph information
+	 *
+	 * @param string $requestType The HTTP method to use, e.g. "GET" or "POST"
+	 * @param string $endpoint    The Graph endpoint to call
+	 *
+	 * @return GraphCollectionRequest The request object, which can be
+	 *                                used to make queries against Graph
+	 * @throws GraphException
+	 */
+    public function createCollectionRequest(string $requestType, string $endpoint): GraphRequest
+    {
+        return new GraphCollectionRequest(
+            $requestType,
+            $endpoint,
+            $this
+        );
+    }
+
+    /**
+     * Return SDK version used in the service library client.
+     *
+     * @return string
+     */
+    public abstract function getSdkVersion(): string;
+
+    /**
+     * Returns API version used in the service library
+     *
+     * @return string
+     */
+    public abstract function getApiVersion(): string;
+}
diff --git a/src/Http/GraphCollectionRequest.php b/src/Http/GraphCollectionRequest.php
index 8512d887..87d6dbb3 100644
--- a/src/Http/GraphCollectionRequest.php
+++ b/src/Http/GraphCollectionRequest.php
@@ -3,30 +3,21 @@
 * Copyright (c) Microsoft Corporation.  All Rights Reserved.
 * Licensed under the MIT License.  See License in the project root
 * for license information.
-*
-* GraphCollectionRequest File
-* PHP version 7
-*
-* @category  Library
-* @package   Microsoft.Graph
-* @copyright 2016 Microsoft Corporation
-* @license   https://opensource.org/licenses/MIT MIT License
-* @version   GIT: 0.1.0
-* @link      https://graph.microsoft.io/
 */
 
 namespace Microsoft\Graph\Http;
 
+use GuzzleHttp\Psr7\Uri;
+use Microsoft\Graph\Exception\GraphClientException;
 use Microsoft\Graph\Exception\GraphException;
 use Microsoft\Graph\Core\GraphConstants;
 
 /**
  * Class GraphCollectionRequest
- *
- * @category Library
- * @package  Microsoft.Graph
- * @license  https://opensource.org/licenses/MIT MIT License
- * @link     https://graph.microsoft.io/
+ * @package Microsoft\Graph\Http
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
  */
 class GraphCollectionRequest extends GraphRequest
 {
@@ -54,12 +45,6 @@ class GraphCollectionRequest extends GraphRequest
     * @var bool
     */
     protected $end;
-    /**
-    * The endpoint that the user called (with query parameters)
-    *
-    * @var string
-    */
-    protected $originalEndpoint;
     /**
      * The return type that the user specified
      *
@@ -68,28 +53,21 @@ class GraphCollectionRequest extends GraphRequest
     protected $originalReturnType;
 
     /**
-    * Constructs a new GraphCollectionRequest object
-    *
-    * @param string $requestType  The HTTP verb for the
-    *                             request ("GET", "POST", "PUT", etc.)
-    * @param string $endpoint     The URI of the endpoint to hit
-    * @param string $accessToken  A valid access token
-    * @param string $baseUrl      The base URL of the request
-    * @param string $apiVersion   The version of the API to call
-    * @param string $proxyPort    The url where to proxy through
-    * @param bool $proxyVerifySSL Whether the proxy requests should perform SSL verification
-    * @throws GraphException when no access token is provided
-    */
-    public function __construct($requestType, $endpoint, $accessToken, $baseUrl, $apiVersion, $proxyPort = null, $proxyVerifySSL = false)
+     * Constructs a new GraphCollectionRequest object
+     *
+     * @param string $requestType The HTTP verb for the request ("GET", "POST", "PUT", etc.)
+     * @param string $endpoint The URI of the endpoint to hit
+     * @param AbstractGraphClient $graphClient
+     * @param string $baseUrl (optional) If empty, it's set to $client's national cloud
+     * @throws GraphClientException
+     */
+    public function __construct(string $requestType, string $endpoint, AbstractGraphClient $graphClient, string $baseUrl = "")
     {
         parent::__construct(
             $requestType,
             $endpoint,
-            $accessToken,
-            $baseUrl,
-            $apiVersion,
-            $proxyPort,
-            $proxyVerifySSL
+            $graphClient,
+            $baseUrl
         );
         $this->end = false;
     }
@@ -98,21 +76,14 @@ public function __construct($requestType, $endpoint, $accessToken, $baseUrl, $ap
 	 * Gets the number of entries in the collection
 	 *
 	 * @return int the number of entries
-	 * @throws GraphException
-	 * @throws \GuzzleHttp\Exception\GuzzleException
-	 */
+     * @throws \Psr\Http\Client\ClientExceptionInterface
+     */
     public function count()
     {
         $query = '$count=true';
-        $request = new GraphRequest(
-            $this->requestType,
-            $this->endpoint . $this->getConcatenator() . $query,
-            $this->accessToken,
-            $this->baseUrl,
-            $this->apiVersion,
-            $this->proxyPort
-        );
-        $result = $request->execute()->getBody();
+        $requestUri = $this->getRequestUri();
+        $this->setRequestUri(new Uri( $requestUri . GraphRequestUtil::getQueryParamConcatenator($requestUri) . $query));
+        $result = $this->execute()->getBody();
 
         if (array_key_exists("@odata.count", $result)) {
             return $result['@odata.count'];
@@ -129,25 +100,25 @@ public function count()
     *
     * @param int $pageSize The page size
     *
-     * @throws GraphException if the requested page size exceeds
+     * @throws GraphClientException if the requested page size exceeds
      *         the Graph's defined page size limit
     * @return GraphCollectionRequest object
     */
-    public function setPageSize($pageSize)
+    public function setPageSize(int $pageSize): self
     {
         if ($pageSize > GraphConstants::MAX_PAGE_SIZE) {
-            throw new GraphException(GraphConstants::MAX_PAGE_SIZE_ERROR);
+            throw new GraphClientException(GraphConstants::MAX_PAGE_SIZE_ERROR);
         }
         $this->pageSize = $pageSize;
         return $this;
     }
 
-	/**
-	 * Gets the next page of results
-	 *
-	 * @return array of objects of class $returnType
-	 * @throws \GuzzleHttp\Exception\GuzzleException
-	 */
+    /**
+     * Gets the next page of results
+     *
+     * @return array of objects of class $returnType
+     * @throws \Psr\Http\Client\ClientExceptionInterface
+     */
     public function getPage()
     {
         $this->setPageCallInfo();
@@ -157,11 +128,11 @@ public function getPage()
     }
 
     /**
-    * Sets the required query information to get a new page
-    *
-    * @return GraphCollectionRequest
-    */
-    public function setPageCallInfo()
+     * Sets the required query information to get a new page
+     *
+     * @return GraphCollectionRequest
+     */
+    public function setPageCallInfo(): self
     {
         // Store these to add temporary query data to request
         $this->originalReturnType = $this->returnType;
@@ -175,11 +146,13 @@ public function setPageCallInfo()
         }
 
         if ($this->nextLink) {
-            $this->endpoint = "/" . implode("/", array_slice(explode("/", $this->nextLink), 4));
+            $this->setRequestUri(new Uri($this->nextLink));
         } else {
             // This is the first request to the endpoint
             if ($this->pageSize) {
-                $this->endpoint .= $this->getConcatenator() . '$top=' . $this->pageSize;
+                $query = '$top='.$this->pageSize;
+                $requestUri = $this->getRequestUri();
+                $this->setRequestUri(new Uri( $requestUri . GraphRequestUtil::getQueryParamConcatenator($requestUri) . $query));
             }
         }
         return $this;
@@ -194,7 +167,7 @@ public function setPageCallInfo()
     * @return mixed result of the call, formatted according
     *         to the returnType set by the user
     */
-    public function processPageCallReturn($response)
+    public function processPageCallReturn(GraphResponse $response)
     {
         $this->nextLink = $response->getNextLink();
         $this->deltaLink = $response->getDeltaLink();
@@ -223,7 +196,7 @@ public function processPageCallReturn($response)
     *
     * @return bool The end
     */
-    public function isEnd()
+    public function isEnd(): bool
     {
         return $this->end;
     }
@@ -234,7 +207,7 @@ public function isEnd()
     *
     * @return string|null The delta link
     */
-    public function getDeltaLink()
+    public function getDeltaLink(): ?string
     {
         return $this->deltaLink;
     }
diff --git a/src/Http/GraphRequest.php b/src/Http/GraphRequest.php
index ec09b371..2da531a9 100644
--- a/src/Http/GraphRequest.php
+++ b/src/Http/GraphRequest.php
@@ -3,72 +3,44 @@
 * Copyright (c) Microsoft Corporation.  All Rights Reserved.
 * Licensed under the MIT License.  See License in the project root
 * for license information.
-*
-* GraphRequest File
-* PHP version 7
-*
-* @category  Library
-* @package   Microsoft.Graph
-* @copyright 2016 Microsoft Corporation
-* @license   https://opensource.org/licenses/MIT MIT License
-* @version   GIT: 0.1.0
-* @link      https://graph.microsoft.io/
 */
 
 namespace Microsoft\Graph\Http;
 
-use GuzzleHttp\Client;
-use GuzzleHttp\Exception\BadResponseException;
+use GuzzleHttp\Psr7\Request;
+use GuzzleHttp\Psr7\Uri;
+use GuzzleHttp\Psr7\Utils;
+use Http\Client\HttpAsyncClient;
+use Http\Promise\Promise;
 use Microsoft\Graph\Core\GraphConstants;
-use Microsoft\Graph\Core\ExceptionWrapper;
+use Microsoft\Graph\Core\NationalCloud;
+use Microsoft\Graph\Exception\GraphClientException;
 use Microsoft\Graph\Exception\GraphException;
+use Psr\Http\Client\ClientExceptionInterface;
+use Psr\Http\Client\ClientInterface;
+use Psr\Http\Message\StreamInterface;
 
 /**
  * Class GraphRequest
- *
- * @category Library
- * @package  Microsoft.Graph
- * @license  https://opensource.org/licenses/MIT MIT License
- * @link     https://graph.microsoft.io/
+ * @package Microsoft\Graph\Http
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
  */
 class GraphRequest
 {
-    /**
-    * A valid access token
-    *
-    * @var string
-    */
-    protected $accessToken;
-    /**
-    * The API version to use ("v1.0", "beta")
-    *
-    * @var string
-    */
-    protected $apiVersion;
-    /**
-    * The base url to call
-    *
-    * @var string
-    */
-    protected $baseUrl;
-    /**
-    * The endpoint to call
-    *
-    * @var string
-    */
-    protected $endpoint;
     /**
     * An array of headers to send with the request
     *
     * @var array(string => string)
     */
-    protected $headers;
+    private $headers;
     /**
     * The body of the request (optional)
     *
     * @var string
     */
-    protected $requestBody;
+    private $requestBody = null;
     /**
     * The type of request to make ("GET", "POST", etc.)
     *
@@ -83,85 +55,69 @@ class GraphRequest
     */
     protected $returnsStream;
     /**
-    * The return type to cast the response as
+    * The object type to cast the response to
     *
-    * @var object|null
+    * @var string
     */
     protected $returnType;
     /**
-    * The timeout, in seconds
-    *
-    * @var int
-    */
-    protected $timeout;
-    /**
-    * The proxy port to use. Null to disable
-    *
-    * @var string
-    */
-    protected $proxyPort;
+     * The Graph client
+     *
+     * @var AbstractGraphClient
+     */
+    private $graphClient;
     /**
-     * Whether SSL verification should be used for proxy requests
+     * PSR-7 Request to be passed to HTTP client
      *
-     * @var bool
+     * @var \GuzzleHttp\Psr7\Request
      */
-    protected $proxyVerifySSL;
+    private $httpRequest;
     /**
-    * Request options to decide if Guzzle Client should throw exceptions when http code is 4xx or 5xx
-    *
-    * @var bool
-    */
-    protected $http_errors;
+     * Full Request URI (base URL + endpoint)
+     *
+     * @var Uri
+     */
+    private $requestUri;
 
     /**
-    * Constructs a new Graph Request object
-    *
-    * @param string $requestType  The HTTP method to use, e.g. "GET" or "POST"
-    * @param string $endpoint     The Graph endpoint to call
-    * @param string $accessToken  A valid access token to validate the Graph call
-    * @param string $baseUrl      The base URL to call
-    * @param string $apiVersion   The API version to use
-    * @param string $proxyPort    The url where to proxy through
-    * @param bool $proxyVerifySSL Whether the proxy requests should perform SSL verification
-    * @throws GraphException when no access token is provided
-    */
-    public function __construct($requestType, $endpoint, $accessToken, $baseUrl, $apiVersion, $proxyPort = null, $proxyVerifySSL = false)
+     * GraphRequest constructor.
+     * Sets $baseUrl by default to $graphClient's national cloud
+     * Resolves $baseUrl and $endpoint based on RFC 3986
+     *
+     * @param string $requestType The HTTP method to use e.g. "GET" or "POST"
+     * @param string $endpoint The url path on the host to be called-
+     * @param AbstractGraphClient $graphClient The Graph client to use
+     * @param string $baseUrl (optional) If empty, it's set to $client's national cloud
+     * @throws GraphClientException
+     */
+    public function __construct(string $requestType, string $endpoint, AbstractGraphClient $graphClient, string $baseUrl = "")
     {
-        $this->requestType = $requestType;
-        $this->endpoint = $endpoint;
-        $this->accessToken = $accessToken;
-        $this->http_errors = true;
-
-        if (!$this->accessToken) {
-            throw new GraphException(GraphConstants::NO_ACCESS_TOKEN);
+        if (!$requestType || !$endpoint || !$graphClient) {
+            throw new GraphClientException("Request type, endpoint and client cannot be null or empty");
         }
-
-        $this->baseUrl = $baseUrl;
-        $this->apiVersion = $apiVersion;
-        $this->timeout = 100;
-        $this->headers = $this->_getDefaultHeaders();
-        $this->proxyPort = $proxyPort;
-        $this->proxyVerifySSL = $proxyVerifySSL;
+        if (!$graphClient->getAccessToken()) {
+            throw new GraphClientException(GraphConstants::NO_ACCESS_TOKEN);
+        }
+        $this->requestType = $requestType;
+        $this->graphClient = $graphClient;
+        $baseUrl = ($baseUrl) ?: $graphClient->getNationalCloud();
+        $this->initRequestUri($baseUrl, $endpoint);
+        $this->initHeaders($baseUrl);
+        $this->initPsr7HttpRequest();
     }
 
-    /**
-     * Gets the Base URL the request is made to
-     *
-     * @return string
-     */
-    public function getBaseUrl()
+    public function getHttpRequest(): Request
     {
-        return $this->baseUrl;
+        return $this->httpRequest;
     }
 
-    /**
-     * Gets the API version in use for the request
-     *
-     * @return string
-     */
-    public function getApiVersion()
-    {
-        return $this->apiVersion;
+    protected function setRequestUri(Uri $uri): void {
+        $this->requestUri = $uri;
+        $this->initPsr7HttpRequest();
+    }
+
+    protected function getRequestUri(): Uri {
+        return $this->requestUri;
     }
 
     /**
@@ -174,41 +130,27 @@ public function getReturnsStream()
         return $this->returnsStream;
     }
 
-    /**
-    * Sets a http errors option
-    *
-    * @param bool $http_errors A bool option to the Graph call
-    *
-    * @return GraphRequest object
-    */
-    public function setHttpErrors($http_errors)
-    {
-        $this->http_errors = $http_errors;
-        return $this;
-    }
-
     /**
     * Sets a new accessToken
     *
     * @param string $accessToken A valid access token to validate the Graph call
     *
-    * @return GraphRequest object
+    * @return $this object
     */
-    public function setAccessToken($accessToken)
+    public function setAccessToken(string $accessToken): self
     {
-        $this->accessToken = $accessToken;
-        $this->headers['Authorization'] = 'Bearer ' . $this->accessToken;
+        $this->addHeaders(['Authorization' => 'Bearer '.$accessToken]);
         return $this;
     }
 
     /**
     * Sets the return type of the response object
     *
-    * @param mixed $returnClass The object class to use
+    * @param string $returnClass The class name to use
     *
-    * @return GraphRequest object
+    * @return $this object
     */
-    public function setReturnType($returnClass)
+    public function setReturnType(string $returnClass): self
     {
         $this->returnType = $returnClass;
         if ($this->returnType == "GuzzleHttp\Psr7\Stream") {
@@ -226,9 +168,10 @@ public function setReturnType($returnClass)
     *
     * @return GraphRequest object
     */
-    public function addHeaders($headers)
+    public function addHeaders(array $headers): self
     {
-        $this->headers = array_merge($this->headers, $headers);
+        $this->headers = array_merge_recursive($this->headers, $headers);
+        $this->initPsr7HttpRequest();
         return $this;
     }
 
@@ -237,7 +180,7 @@ public function addHeaders($headers)
     *
     * @return array of headers
     */
-    public function getHeaders()
+    public function getHeaders(): array
     {
         return $this->headers;
     }
@@ -246,27 +189,28 @@ public function getHeaders()
     * Attach a body to the request. Will JSON encode
     * any Microsoft\Graph\Model objects as well as arrays
     *
-    * @param mixed $obj The object to include in the request
+    * @param string|StreamInterface|object $obj The object to include in the request
     *
-    * @return GraphRequest object
+    * @return $this object
     */
-    public function attachBody($obj)
+    public function attachBody($obj): self
     {
         // Attach streams & JSON automatically
-        if (is_string($obj) || is_a($obj, 'GuzzleHttp\\Psr7\\Stream')) {
+        if (is_string($obj) || is_a($obj, StreamInterface::class)) {
             $this->requestBody = $obj;
         }
         // By default, JSON-encode
         else {
             $this->requestBody = json_encode($obj);
         }
+        $this->initPsr7HttpRequest();
         return $this;
     }
 
     /**
     * Get the body of the request
     *
-    * @return mixed request body of any type
+    * @return string|StreamInterface request body
     */
     public function getBody()
     {
@@ -274,56 +218,19 @@ public function getBody()
     }
 
     /**
-    * Sets the timeout limit of the cURL request
-    *
-    * @param int $timeout The timeout in seconds
-    *
-    * @return GraphRequest object
-    */
-    public function setTimeout($timeout)
-    {
-        $this->timeout = $timeout;
-        return $this;
-    }
-
-    /**
-     * Gets the timeout value of the request
+     * Executes the HTTP request using $graphClient's http client or a PSR-18 compliant HTTP client
      *
-     * @return int
+     * @param ClientInterface|null $client (optional) When null, uses $graphClient's http client
+     * @return array|GraphResponse|StreamInterface|object Graph Response object or response body cast to $returnType
+     * @throws ClientExceptionInterface
      */
-    public function getTimeout()
-    {
-        return $this->timeout;
-    }
-
-    /**
-    * Executes the HTTP request using Guzzle
-    *
-    * @param mixed $client The client to use in the request
-    *
-    * @throws \GuzzleHttp\Exception\GuzzleException
-    *
-    * @return mixed object or array of objects
-    *         of class $returnType
-    */
-    public function execute($client = null)
+    public function execute(?ClientInterface $client = null)
     {
         if (is_null($client)) {
-            $client = $this->createGuzzleClient();
+            $client = $this->graphClient->getHttpClient();
         }
 
-        try {
-            $result = $client->request(
-                $this->requestType,
-                $this->_getRequestUrl(),
-                [
-                    'body' => $this->requestBody,
-                    'timeout' => $this->timeout
-                ]
-            );
-        } catch(BadResponseException $e) {
-            throw ExceptionWrapper::wrapGuzzleBadResponseException($e);
-        }
+        $result = $client->sendRequest($this->httpRequest);
 
         // Check to see if returnType is a stream, if so return it immediately
         if($this->returnsStream) {
@@ -348,27 +255,19 @@ public function execute($client = null)
     }
 
     /**
-    * Executes the HTTP request asynchronously using Guzzle
-    *
-    * @param mixed $client The client to use in the request
-    *
-    * @return mixed object or array of objects
-    *         of class $returnType
-    */
-    public function executeAsync($client = null)
+     * Executes the HTTP request asynchronously using $client
+     *
+     * @param HttpAsyncClient|null $client (optional) When null, uses $graphClient's http client
+     * @return Promise Resolves to GraphResponse object|response body cast to $returnType. Fails throwing the exception
+     * @throws \Exception when promise fails
+     */
+    public function executeAsync(?HttpAsyncClient $client = null): Promise
     {
         if (is_null($client)) {
-            $client = $this->createGuzzleClient();
+            $client = $this->graphClient->getHttpClient();
         }
 
-        $promise = $client->requestAsync(
-            $this->requestType,
-            $this->_getRequestUrl(),
-            [
-                'body' => $this->requestBody,
-                'timeout' => $this->timeout
-            ]
-        )->then(
+        return $client->sendAsyncRequest($this->httpRequest)->then(
             // On success, return the result/response
             function ($result) {
 
@@ -391,163 +290,99 @@ function ($result) {
                 }
                 return $returnObject;
             },
-            // On fail, log the error and return null
+            // On fail, forward the exception
             function ($reason) {
-                if ($reason instanceof BadResponseException) {
-                    $reason = ExceptionWrapper::wrapGuzzleBadResponseException($reason);
-                }
-                trigger_error("Async call failed: " . $reason->getMessage());
-                return null;
+                throw $reason;
             }
         );
-        return $promise;
     }
 
     /**
-    * Download a file from OneDrive to a given location
-    *
-    * @param string $path   The path to download the file to
-    * @param mixed  $client The client to use in the request
-    *
-    * @throws GraphException if file path is invalid
-    * @throws \GuzzleHttp\Exception\GuzzleException
-    *
-    * @return null
-    */
-    public function download($path, $client = null)
+     * Download a file from OneDrive to a given location
+     *
+     * @param string $path path to download the file contents to
+     * @param ClientInterface|null $client (optional) When null, defaults to $graphClient's http client
+     * @throws ClientExceptionInterface|GraphClientException when unable to open $path for writing
+     */
+    public function download(string $path, ?ClientInterface $client = null): void
     {
         if (is_null($client)) {
-            $client = $this->createGuzzleClient();
+            $client = $this->graphClient->getHttpClient();
         }
         try {
-            $file = fopen($path, 'w');
-            if (!$file) {
-                throw new GraphException(GraphConstants::INVALID_FILE);
-            }
-
-            $client->request(
-                $this->requestType,
-                $this->_getRequestUrl(),
-                [
-                    'body' => $this->requestBody,
-                    'sink' => $file,
-                    'timeout' => $this->timeout
-                ]
-            );
-            if(is_resource($file)){
-                fclose($file);
-            }
-
-        } catch(GraphException $e) {
-            throw new GraphException(GraphConstants::INVALID_FILE);
-        } catch(BadResponseException $e) {
-            throw ExceptionWrapper::wrapGuzzleBadResponseException($e);
+            $resource = Utils::tryFopen($path, 'w');
+            $stream = Utils::streamFor($resource);
+            $response = $client->sendRequest($this->httpRequest);
+            $stream->write($response->getBody());
+            $stream->close();
+        } catch (\RuntimeException $ex) {
+            throw new GraphClientException(GraphConstants::INVALID_FILE, $ex->getCode(), $ex);
         }
-
-        return null;
     }
 
     /**
-    * Upload a file to OneDrive from a given location
-    *
-    * @param string $path   The path of the file to upload
-    * @param mixed  $client The client to use in the request
-    *
-    * @throws GraphException if file is invalid
-    * @throws \GuzzleHttp\Exception\GuzzleException
-    *
-    * @return mixed DriveItem or array of DriveItems
-    */
-    public function upload($path, $client = null)
+     * Upload a file from $path to Graph API
+     *
+     * @param string $path path of file to be uploaded
+     * @param ClientInterface|null $client (optional)
+     * @return array|GraphResponse|StreamInterface|object Graph Response object or response body cast to $returnType
+     * @throws ClientExceptionInterface|GraphClientException if $path cannot be opened for reading
+     */
+    public function upload(string $path, ?ClientInterface $client = null)
     {
         if (is_null($client)) {
-            $client = $this->createGuzzleClient();
+            $client = $this->graphClient->getHttpClient();
         }
         try {
-            if (file_exists($path) && is_readable($path)) {
-                $file = fopen($path, 'r');
-                $stream = \GuzzleHttp\Psr7\Utils::streamFor($file);
-                $this->requestBody = $stream;
-                return $this->execute($client);
-            } else {
-                throw new GraphException(GraphConstants::INVALID_FILE);
-            }
-        } catch(GraphException $e) {
-            throw new GraphException(GraphConstants::INVALID_FILE);
+            $resource = Utils::tryFopen($path, 'r');
+            $stream = Utils::streamFor($resource);
+            $this->attachBody($stream);
+            return $this->execute($client);
+        } catch(\RuntimeException $e) {
+            throw new GraphClientException(GraphConstants::INVALID_FILE, $e->getCode(), $e->getPrevious());
         }
     }
 
     /**
-    * Get a list of headers for the request
-    *
-    * @return array The headers for the request
-    */
-    private function _getDefaultHeaders()
-    {
-        $headers = [
-            'Host' => $this->baseUrl,
-            'Content-Type' => 'application/json',
-            'SdkVersion' => 'Graph-php-' . GraphConstants::SDK_VERSION,
-            'Authorization' => 'Bearer ' . $this->accessToken
-        ];
-        return $headers;
-    }
-
-    /**
-    * Get the concatenated request URL
-    *
-    * @return string request URL
-    */
-    private function _getRequestUrl()
+     * Sets default headers based on baseUrl being a Graph endpoint or not
+     */
+    private function initHeaders(string $baseUrl): void
     {
-        //Send request with opaque URL
-        if (stripos($this->endpoint, "http") === 0) {
-            return $this->endpoint;
+        $coreSdkVersion = "graph-php-core/".GraphConstants::SDK_VERSION;
+        $serviceLibSdkVersion = "Graph-php-".$this->graphClient->getSdkVersion();
+        if (NationalCloud::containsNationalCloudHost($baseUrl)) {
+            $this->headers = [
+                'Content-Type' => 'application/json',
+                'SdkVersion' => $coreSdkVersion.", ".$serviceLibSdkVersion,
+                'Authorization' => 'Bearer ' . $this->graphClient->getAccessToken()
+            ];
+        } else {
+            $this->headers = [
+                'Content-Type' => 'application/json',
+            ];
         }
-
-        return $this->apiVersion . $this->endpoint;
     }
 
     /**
-    * Checks whether the endpoint currently contains query
-    * parameters and returns the relevant concatenator for
-    * the new query string
-    *
-    * @return string "?" or "&"
-    */
-    protected function getConcatenator()
-    {
-        if (stripos($this->endpoint, "?") === false) {
-            return "?";
+     * Creates full request URI by resolving $baseUrl and $endpoint based on RFC 3986
+     *
+     * @param string $baseUrl
+     * @param $endpoint
+     * @throws GraphClientException
+     */
+    protected function initRequestUri(string $baseUrl, $endpoint): void {
+        try {
+            $this->requestUri = GraphRequestUtil::getRequestUri($baseUrl, $endpoint, $this->graphClient->getApiVersion());
+            if (!$this->requestUri) {
+                // $endpoint is a full URL but doesn't meet criteria
+                throw new GraphClientException("Endpoint is not a valid URL. Must contain national cloud host.");
+            }
+        } catch (\InvalidArgumentException $ex) {
+            throw new GraphClientException("Unable to resolve base URL=".$baseUrl."\" with endpoint=".$endpoint."\"", 0, $ex);
         }
-        return "&";
     }
 
-    /**
-    * Create a new Guzzle client
-    * To allow for user flexibility, the
-    * client is not reused. This allows the user
-    * to set and change headers on a per-request
-    * basis
-    *
-    * If a proxyPort was passed in the constructor, all
-    * requests will be forwared through this proxy.
-    *
-    * @return \GuzzleHttp\Client The new client
-    */
-    protected function createGuzzleClient()
-    {
-        $clientSettings = [
-            'base_uri' => $this->baseUrl,
-            'http_errors' => $this->http_errors,
-            'headers' => $this->headers
-        ];
-        if ($this->proxyPort !== null) {
-            $clientSettings['verify'] = $this->proxyVerifySSL;
-            $clientSettings['proxy'] = $this->proxyPort;
-        }
-        $client = new Client($clientSettings);
-
-        return $client;
+    protected function initPsr7HttpRequest(): void {
+        $this->httpRequest = new Request($this->requestType, $this->requestUri, $this->headers, $this->requestBody);
     }
 }
diff --git a/src/Http/GraphRequestUtil.php b/src/Http/GraphRequestUtil.php
new file mode 100644
index 00000000..94dd15e3
--- /dev/null
+++ b/src/Http/GraphRequestUtil.php
@@ -0,0 +1,53 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ */
+
+
+namespace Microsoft\Graph\Http;
+
+use GuzzleHttp\Psr7\Uri;
+use GuzzleHttp\Psr7\UriResolver;
+use Microsoft\Graph\Core\NationalCloud;
+use Psr\Http\Message\UriInterface;
+
+/**
+ * Class GraphRequestUtil
+ * @package Microsoft\Graph\Http
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
+ */
+class GraphRequestUtil
+{
+    /**
+     * Returns full request URI by resolving $baseUrl and $endpoint based on RFC 3986
+     * Prepends $apiVersion to $endpoint if $baseUrl contains a national cloud host
+     * $endpoint can be a full URI with a national cloud host
+     *
+     * @param string $baseUrl if empty, is overwritten with $client's national cloud
+     * @param string $endpoint can be a full URL
+     * @param string $apiVersion
+     * @return UriInterface|null
+     */
+    public static function getRequestUri(string $baseUrl, string $endpoint, string $apiVersion = "v1.0"): ?UriInterface {
+        // If endpoint is a full url, ensure the host is a national cloud or custom host
+        if (parse_url($endpoint, PHP_URL_SCHEME)) {
+            return (NationalCloud::containsNationalCloudHost($endpoint)) ? new Uri($endpoint) : null;
+        }
+        $relativeUrl = (NationalCloud::containsNationalCloudHost($baseUrl)) ? "/".$apiVersion : "";
+        $relativeUrl .= (substr($endpoint, 0, 1) == "/") ? $endpoint : "/".$endpoint;
+        return UriResolver::resolve(new Uri($baseUrl), new Uri($relativeUrl));
+    }
+
+    /**
+     * Determine correct symbol to add before concatenating query parameters to $url
+     * @param Uri $url
+     * @return string
+     */
+    public static function getQueryParamConcatenator(Uri $url): string {
+        return stripos($url, "?") ? "&" : "?";
+    }
+}
diff --git a/src/Http/HttpClientFactory.php b/src/Http/HttpClientFactory.php
new file mode 100644
index 00000000..4a5a503f
--- /dev/null
+++ b/src/Http/HttpClientFactory.php
@@ -0,0 +1,166 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ */
+
+namespace Microsoft\Graph\Http;
+
+use GuzzleHttp\Client;
+use GuzzleHttp\RequestOptions;
+use Http\Adapter\Guzzle7\Client as GuzzleAdapter;
+use Http\Promise\Promise;
+use Microsoft\Graph\Core\NationalCloud;
+use Microsoft\Graph\Exception\GraphClientException;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+/**
+ * Class HttpClientFactory
+ *
+ * Configures a Guzzle HTTP client for use with Graph API
+ *
+ * @package Microsoft\Graph\Http
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
+ */
+final class HttpClientFactory
+{
+    /**
+     * @var int Default connection timeout
+     */
+    const CONNECTION_TIMEOUT_SEC = 30;
+
+    /**
+     * @var int Default request timeout
+     */
+    const REQUEST_TIMEOUT_SEC = 100;
+
+    /**
+     * @var string Graph API host to use as base URL and for authentication
+     */
+    private static $nationalCloud = NationalCloud::GLOBAL;
+
+    /**
+     * @var array Guzzle client config options (https://docs.guzzlephp.org/en/stable/quickstart.html#creating-a-client)
+     */
+    private static $clientConfig = [];
+
+    /**
+     * @var HttpClientFactory|null Store singleton instance of the HttpClientFactory
+     */
+    private static $instance = null;
+
+    /**
+     * HttpClientFactory constructor.
+     * Creates only one instance to be reused in the static methods
+     */
+    private function __construct() {
+        if (!self::$instance) {
+            self::$instance = new HttpClientFactory();
+        }
+        return self::$instance;
+    }
+
+    /**
+     * Set national cloud to be used as the base URL
+     *
+     * @param string $nationalCloud
+     * @return $this
+     * @throws GraphClientException if $nationalCloud is empty or an invalid national cloud Host
+     */
+    public static function nationalCloud(string $nationalCloud = NationalCloud::GLOBAL): HttpClientFactory {
+        if (!$nationalCloud || !NationalCloud::containsNationalCloudHost($nationalCloud)) {
+            throw new GraphClientException("Invalid national cloud passed. See https://docs.microsoft.com/en-us/graph/deployments#microsoft-graph-and-graph-explorer-service-root-endpoints.");
+        }
+        self::$nationalCloud = $nationalCloud;
+        return new HttpClientFactory();
+    }
+
+    /**
+     * Set configuration options for the Guzzle client
+     *
+     * @param array $config
+     * @return $this
+     */
+    public static function clientConfig(array $config): HttpClientFactory {
+        self::$clientConfig = $config;
+        return new HttpClientFactory();
+    }
+
+    /**
+     * Creates a Guzzle client with the custom configs provided or a default client if no config was given
+     * Creates default Guzzle client if no custom configs were passed
+     *
+     * @return \GuzzleHttp\Client
+     */
+    public static function create(): \GuzzleHttp\Client {
+        if (!self::$clientConfig) {
+            return new Client(self::getDefaultConfig());
+        }
+        self::mergeConfig();
+        return new Client(self::$clientConfig);
+    }
+
+    /**
+     * Creates an HttpClientInterface implementation that wraps around a Guzzle client
+     *
+     * @return HttpClientInterface
+     */
+    public static function createAdapter(): HttpClientInterface {
+        return new class(self::create()) implements HttpClientInterface {
+            private $clientAdapter;
+
+            public function __construct(Client $guzzleClient) {
+                $this->clientAdapter = new GuzzleAdapter($guzzleClient);
+            }
+
+            public function sendRequest(RequestInterface $request): ResponseInterface {
+                return $this->clientAdapter->sendRequest($request);
+            }
+
+            public function sendAsyncRequest(RequestInterface $request): Promise {
+                return $this->clientAdapter->sendAsyncRequest($request);
+            }
+        };
+    }
+
+    /**
+     * Returns Graph-specific config for Guzzle
+     *
+     * @return array
+     */
+    private static function getDefaultConfig(): array {
+        return [
+            RequestOptions::CONNECT_TIMEOUT => self::CONNECTION_TIMEOUT_SEC,
+            RequestOptions::TIMEOUT => self::REQUEST_TIMEOUT_SEC,
+            RequestOptions::HEADERS => [
+                "Content-Type" => "application/json"
+            ],
+            RequestOptions::HTTP_ERRORS => false,
+            "base_uri" => self::$nationalCloud
+        ];
+    }
+
+    /**
+     * Merges client defined config array with Graph's default config.
+     * Provides defaults for timeouts and headers if none have been provided.
+     * Overrides base_uri.
+     */
+    private static function mergeConfig(): void {
+        $defaultConfig = self::getDefaultConfig();
+
+        if (!isset(self::$clientConfig[RequestOptions::CONNECT_TIMEOUT])) {
+            self::$clientConfig[RequestOptions::CONNECT_TIMEOUT] = $defaultConfig[RequestOptions::CONNECT_TIMEOUT];
+        }
+        if (!isset(self::$clientConfig[RequestOptions::TIMEOUT])) {
+            self::$clientConfig[RequestOptions::TIMEOUT] = $defaultConfig[RequestOptions::TIMEOUT];
+        }
+        if (!isset(self::$clientConfig[RequestOptions::HEADERS])) {
+            self::$clientConfig[RequestOptions::HEADERS] = $defaultConfig[RequestOptions::HEADERS];
+        }
+        self::$clientConfig["base_uri"] = self::$nationalCloud;
+    }
+}
diff --git a/src/Http/HttpClientInterface.php b/src/Http/HttpClientInterface.php
new file mode 100644
index 00000000..e5c83d85
--- /dev/null
+++ b/src/Http/HttpClientInterface.php
@@ -0,0 +1,26 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ */
+
+namespace Microsoft\Graph\Http;
+
+use Http\Client\HttpAsyncClient;
+use Http\Client\HttpClient;
+
+/**
+ * Interface HttpClientInterface
+ *
+ * Provides methods for making synchronous and asynchronous requests on an HTTP client
+ *
+ * @package Microsoft\Graph\Http
+ * @copyright 2021 Microsoft Corporation
+ * @license https://opensource.org/licenses/MIT MIT License
+ * @link https://developer.microsoft.com/graph
+ */
+interface HttpClientInterface extends HttpClient, HttpAsyncClient
+{
+
+}
diff --git a/tests/Core/ExceptionWrapperTest.php b/tests/Core/ExceptionWrapperTest.php
deleted file mode 100644
index 5079c822..00000000
--- a/tests/Core/ExceptionWrapperTest.php
+++ /dev/null
@@ -1,91 +0,0 @@
-<?php
-use GuzzleHttp\Exception\BadResponseException;
-use GuzzleHttp\Psr7\Request;
-use GuzzleHttp\Psr7\Response;
-use Microsoft\Graph\Core\ExceptionWrapper;
-use PHPUnit\Framework\TestCase;
-
-class ExceptionWrapperTest extends TestCase
-{
-    protected $responseBodies;
-    protected $autoBadResponseExceptions;
-    protected $manualBadResponseExceptions;
-
-    public function setUp(): void
-    {
-        $this->responseBodies = array(
-            'short' => json_encode(array('body' => 'content')), // not truncated by Guzzle
-            'long' => json_encode(array('body' => base64_encode(random_bytes(120)) . '.')), // truncated by Guzzle
-        );
-
-        $this->autoBadResponseExceptions = array();
-        $this->manualBadResponseExceptions = array();
-        foreach ($this->responseBodies as $name => $responseBody) {
-            $autoBadResponseException = GuzzleHttp\Exception\RequestException::create(new Request("GET", "/endpoint"), new Response(400, [], $responseBody));
-            assert($autoBadResponseException instanceof BadResponseException);
-            $this->autoBadResponseExceptions[$name] = $autoBadResponseException;
-
-            $manualBadResponseException = new BadResponseException("Error: API returned 400", new Request("GET", "/endpoint"), new Response(400, [], $responseBody));
-            $this->manualBadResponseExceptions[$name] = $manualBadResponseException;
-        }
-    }
-
-    public function testWrapBadResponseExceptionReturnsInstanceOfSameClass()
-    {
-        $name = 'short';
-
-        $ex = $this->autoBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertInstanceOf(get_class($ex), $wrappedException);
-
-        $ex = $this->manualBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertInstanceOf(get_class($ex), $wrappedException);
-
-        $name = 'long';
-
-        $ex = $this->autoBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertInstanceOf(get_class($ex), $wrappedException);
-
-        $ex = $this->manualBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertInstanceOf(get_class($ex), $wrappedException);
-    }
-
-    public function testWrapAutoBadResponseExceptionHasResponseBody()
-    {
-        $name = 'short';
-        $responseBody = $this->responseBodies[$name];
-        $ex = $this->autoBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertStringContainsString($responseBody, $wrappedException->getMessage());
-
-        $name = 'long';
-        $responseBody = $this->responseBodies[$name];
-        $ex = $this->autoBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertStringContainsString($responseBody, $wrappedException->getMessage());
-    }
-
-    public function testWrapManualBadResponseExceptionHasNotResponseBody()
-    {
-        $name = 'short';
-        $responseBody = $this->responseBodies[$name];
-        $ex = $this->manualBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertStringNotContainsString($responseBody, $wrappedException->getMessage());
-
-        $name = 'long';
-        $responseBody = $this->responseBodies[$name];
-        $ex = $this->manualBadResponseExceptions[$name];
-        $wrappedException = ExceptionWrapper::wrapGuzzleBadResponseException($ex);
-        $this->assertStringNotContainsString($responseBody, $wrappedException->getMessage());
-    }
-
-    public function testWrapBadResponseExceptionWithInvalidInput()
-    {
-        $this->expectException(TypeError::class);
-        ExceptionWrapper::wrapGuzzleBadResponseException(null);
-    }
-}
diff --git a/tests/Core/NationalCloudTest.php b/tests/Core/NationalCloudTest.php
new file mode 100644
index 00000000..ff3cae8d
--- /dev/null
+++ b/tests/Core/NationalCloudTest.php
@@ -0,0 +1,55 @@
+<?php
+
+
+namespace Core;
+
+
+use Microsoft\Graph\Core\NationalCloud;
+
+class NationalCloudTest extends \PHPUnit\Framework\TestCase
+{
+    function testNationalCloudConstantsAreValid() {
+        $nationalClouds = array_values((new \ReflectionClass(NationalCloud::class))->getConstants());
+        foreach ($nationalClouds as $nationalCloud) {
+            $this->assertTrue(NationalCloud::containsNationalCloudHost($nationalCloud));
+        }
+    }
+
+    function testNationalCloudWithPortIsValid() {
+        $this->assertTrue(NationalCloud::containsNationalCloudHost(NationalCloud::GLOBAL.":1234"));
+    }
+
+    function testNationalCloudWithTrailingForwardSlashIsValid() {
+        $this->assertTrue(NationalCloud::containsNationalCloudHost(NationalCloud::GLOBAL."/"));
+    }
+
+    function testNationalCloudWithPathIsValid() {
+        $this->assertTrue(NationalCloud::containsNationalCloudHost(NationalCloud::GLOBAL."/v1.0/"));
+    }
+
+    function testContainsNationalCloudWithCapitalisedHost() {
+        $url = "https://GRAPH.microsoft.COM";
+        self::assertTrue(NationalCloud::containsNationalCloudHost($url));
+    }
+
+    function testEmptyNationalCloudUrlInvalid() {
+        $this->assertFalse(NationalCloud::containsNationalCloudHost(""));
+    }
+
+    function testNullNationalCloudThrowsError() {
+        $this->expectException(\TypeError::class);
+        NationalCloud::containsNationalCloudHost(null);
+    }
+
+    function testInvalidNationalCloud() {
+        $this->assertFalse(NationalCloud::containsNationalCloudHost("https://www.microsoft.com"));
+    }
+
+    function testNationalCloudWithoutSchemeInvalid() {
+        $this->assertFalse(NationalCloud::containsNationalCloudHost("graph.microsoft.com"));
+    }
+
+    function testMalformedNationalCloudInvalid() {
+        $this->assertFalse(NationalCloud::containsNationalCloudHost("https:///"));
+    }
+}
diff --git a/tests/Exception/ExceptionTest.php b/tests/Exception/ExceptionTest.php
index 39520e09..8086b42e 100644
--- a/tests/Exception/ExceptionTest.php
+++ b/tests/Exception/ExceptionTest.php
@@ -1,6 +1,7 @@
 <?php
 use PHPUnit\Framework\TestCase;
 use Microsoft\Graph\Exception\GraphException;
+use Microsoft\Graph\Exception\GraphClientException;
 
 class ExceptionTest extends TestCase
 {
@@ -9,4 +10,9 @@ public function testToString()
         $exception = new GraphException('bad stuff', '404');
         $this->assertEquals("Microsoft\Graph\Exception\GraphException: [404]: bad stuff\n", $exception->__toString());
     }
-}
\ No newline at end of file
+
+    public function testChildExceptionClassToString() {
+        $exception = new GraphClientException("Invalid national cloud");
+        $this->assertStringContainsString(get_class($exception), $exception);
+    }
+}
diff --git a/tests/GraphTest.php b/tests/GraphTest.php
index 8cc0745d..86c8919d 100644
--- a/tests/GraphTest.php
+++ b/tests/GraphTest.php
@@ -44,7 +44,7 @@ public function testRequestWithCustomEndpoint()
         $graph->setBaseUrl('url2');
 
         $request = $graph->createRequest("GET", "/me");
-        $this->assertEquals('url2', $request->getBaseUrl());
+        $this->assertEquals('url2', $request->getNationalCloud());
     }
 
     public function testBetaRequest()
@@ -72,4 +72,4 @@ public function testMultipleGraphObjects()
         $this->assertEquals(GraphConstants::API_VERSION, $request->getApiVersion());
         $this->assertEquals('beta', $request2->getApiVersion());
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Http/GraphRequestUtilTest.php b/tests/Http/GraphRequestUtilTest.php
new file mode 100644
index 00000000..21c55d8f
--- /dev/null
+++ b/tests/Http/GraphRequestUtilTest.php
@@ -0,0 +1,104 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ */
+
+namespace Http;
+
+
+use GuzzleHttp\Psr7\Uri;
+use Microsoft\Graph\Core\NationalCloud;
+use Microsoft\Graph\Http\AbstractGraphClient;
+use Microsoft\Graph\Http\GraphRequestUtil;
+
+class GraphRequestUtilTest extends \PHPUnit\Framework\TestCase
+{
+    private $apiVersion;
+
+    function setUp(): void {
+        $graphClient = (new class extends AbstractGraphClient {
+            public function getSdkVersion(): string {
+                return "";
+            }
+
+            public function getApiVersion(): string {
+                return "v1.0";
+            }
+        });
+        $this->apiVersion = $graphClient->getApiVersion();
+    }
+
+    function testGetRequestUriWithFullNationalCloudEndpointUrlReturnsUri() {
+        $endpoint = NationalCloud::GLOBAL."/me/events?\$skip=100&\$top=10";
+        $result = GraphRequestUtil::getRequestUri("", $endpoint, $this->apiVersion);
+        self::assertEquals($endpoint, strval($result));
+    }
+
+    function testGetRequestUriWithFullNonNationalCloudEndpointReturnsNull() {
+        $endpoint = "https://www.outlook.com/mail?user=me";
+        $uri = GraphRequestUtil::getRequestUri("", $endpoint, $this->apiVersion);
+        self::assertNull($uri);
+    }
+
+    function testGetRequestUriWithValidBaseUrlResolvesCorrectly() {
+        $validBaseUrls = [
+            "https://graph.microsoft.com",
+            "https://graph.microsoft.com/",
+            "https://graph.microsoft.com/beta",
+            "https://graph.microsoft.com/v1.0/"
+        ];
+        $endpoints = ["/me/events", "me/events"];
+        $expected = "https://graph.microsoft.com/v1.0/me/events";
+        foreach ($validBaseUrls as $baseUrl) {
+            foreach ($endpoints as $endpoint) {
+                $uri = GraphRequestUtil::getRequestUri($baseUrl, $endpoint, $this->apiVersion);
+                self::assertEquals($expected, strval($uri));
+            }
+        }
+    }
+
+    function testGetRequestUriWithEmptyBaseUriUsesNationalCloudByDefault() {
+        $endpoints= ["/me/events", "me/events"];
+        $expected = "https://graph.microsoft.com/v1.0/me/events";
+        foreach ($endpoints as $endpoint) {
+            $uri = GraphRequestUtil::getRequestUri("", $endpoint, $this->apiVersion);
+            self::assertEquals($expected, strval($uri));
+        }
+    }
+
+    function testGetRequestUriWithoutNationalCloudHostDoesntSetApiVersion() {
+        $baseUrl = "https://outlook.microsoft.com/mail/";
+        $endpoint = "?startDate=2020-10-02&sort=desc";
+        $expected = $baseUrl.$endpoint;
+        $uri = GraphRequestUtil::getRequestUri($baseUrl, $endpoint, $this->apiVersion);
+        self::assertEquals($expected, strval($uri));
+
+    }
+
+    function testGetRequestUriWithInvalidFullEndpointUrlThrowsException() {
+        $this->expectException(\InvalidArgumentException::class);
+        $endpoint = "http:/microsoft.com:localhost\$endpoint";
+        $uri = GraphRequestUtil::getRequestUri("", $endpoint, $this->apiVersion);
+    }
+
+    function testGetRequestUrlWithInvalidBaseUrlAndEndpointThrowsException() {
+        $this->expectException(\InvalidArgumentException::class);
+        $baseUrl = "https://graph.microsoft.com";
+        $endpoint = "http:/microsoft.com:localhost\$endpoint";
+        $uri = GraphRequestUtil::getRequestUri($baseUrl, $endpoint, $this->apiVersion);
+    }
+
+    function testGetQueryParamConcatenatorWithExistingQueryParams() {
+        $uri = new Uri("https://graph.microsoft.com?\$skip=10");
+        $result = GraphRequestUtil::getQueryParamConcatenator($uri);
+        self::assertEquals("&", $result);
+    }
+
+    function testGetQueryParamConcatenatorWithoutQueryParams() {
+        $uri = new Uri("https://graph.microsoft.com");
+        $result = GraphRequestUtil::getQueryParamConcatenator($uri);
+        self::assertEquals("?", $result);
+    }
+}
diff --git a/tests/Http/HttpClientFactoryTest.php b/tests/Http/HttpClientFactoryTest.php
new file mode 100644
index 00000000..2f214349
--- /dev/null
+++ b/tests/Http/HttpClientFactoryTest.php
@@ -0,0 +1,43 @@
+<?php
+
+
+namespace Http;
+
+
+use Microsoft\Graph\Core\NationalCloud;
+use Microsoft\Graph\Exception\GraphClientException;
+use Microsoft\Graph\Http\HttpClientFactory;
+use Microsoft\Graph\Http\HttpClientInterface;
+
+class HttpClientFactoryTest extends \PHPUnit\Framework\TestCase
+{
+    function testNationalCloudWithEmptyString() {
+        $this->expectException(GraphClientException::class);
+        HttpClientFactory::nationalCloud("");
+    }
+
+    function testNationalCloudWithInvalidUrl() {
+        $this->expectException(GraphClientException::class);
+        HttpClientFactory::nationalCloud("https://www.microsoft.com");
+    }
+
+    function testCreateWithNoConfigReturnsDefaultClient() {
+        $client = HttpClientFactory::create();
+        $this->assertInstanceOf(\GuzzleHttp\Client::class, $client);
+    }
+
+    function testCreateWithConfigCreatesClient() {
+        $config = [
+            "proxy" => "localhost:8000",
+            "verify" => false
+        ];
+        $client = HttpClientFactory::clientConfig($config)::nationalCloud(NationalCloud::GERMANY)::create();
+        $this->assertInstanceOf(\GuzzleHttp\Client::class, $client);
+    }
+
+    function testCreateAdapterReturnsHttpClientInterface() {
+        $adapter = HttpClientFactory::nationalCloud(NationalCloud::US_DOD)::createAdapter();
+        $this->assertInstanceOf(HttpClientInterface::class, $adapter);
+    }
+
+}