diff --git a/changes/perserve-styles.feature b/changes/perserve-styles.feature
new file mode 100644
index 0000000..9f15f5d
--- /dev/null
+++ b/changes/perserve-styles.feature
@@ -0,0 +1 @@
+Optionally preserve styles with the same id of appended documents. [buchi]
\ No newline at end of file
diff --git a/docxcompose/command.py b/docxcompose/command.py
index 0b2e253..be50f73 100644
--- a/docxcompose/command.py
+++ b/docxcompose/command.py
@@ -27,6 +27,11 @@ def setup_parser():
         help="path to the output file",
         metavar="file",
     )
+    parser.add_argument(
+        "--preserve-styles",
+        action="store_true",
+        default=False,
+    )
     return parser
 
 
@@ -46,7 +51,10 @@ def parse_args(parser, args):
 
 
 def compose_files(parser, parsed_args):
-    composer = Composer(Document(parsed_args.master))
+    options = {
+        "preserve_styles": parsed_args.preserve_styles,
+    }
+    composer = Composer(Document(parsed_args.master), **options)
     for slave_path in parsed_args.files:
         composer.append(Document(slave_path))
 
diff --git a/docxcompose/composer.py b/docxcompose/composer.py
index 05a1088..72cb754 100644
--- a/docxcompose/composer.py
+++ b/docxcompose/composer.py
@@ -15,7 +15,9 @@
 
 from docxcompose.image import ImageWrapper
 from docxcompose.properties import CustomProperties
+from docxcompose.utils import increment_name
 from docxcompose.utils import NS
+from docxcompose.utils import xml_elements_equal
 from docxcompose.utils import xpath
 
 
@@ -34,13 +36,22 @@
     RT.FOOTNOTES,
 ]
 
+IGNORED_STYLE_TAGS = set(
+    [
+        "{http://schemas.openxmlformats.org/wordprocessingml/2006/main}name",
+        "{http://schemas.openxmlformats.org/wordprocessingml/2006/main}rsid",
+    ]
+)
+
 
 class Composer(object):
-    def __init__(self, doc):
+    def __init__(self, doc, preserve_styles=False):
         self.doc = doc
         self.pkg = doc.part.package
 
         self.restart_numbering = True
+        self.preserve_styles = preserve_styles
+        self._preserved_styles = {}
 
         self.reset_reference_mapping()
 
@@ -59,6 +70,7 @@ def append(self, doc, remove_property_fields=True):
     def insert(self, index, doc, remove_property_fields=True):
         """Insert the given document at the given index."""
         self.reset_reference_mapping()
+        self._current_preserved_styles = {}
 
         # Remove custom property fields but keep the values
         if remove_property_fields:
@@ -299,24 +311,61 @@ def add_styles(self, doc, element):
 
         for style_id in used_style_ids:
             our_style_id = self.mapped_style_id(style_id)
-            if our_style_id not in our_style_ids:
+            # To preserve styles with the same id from added documents, we
+            # create a copy and append a suffix to the id and name.
+            if self.preserve_styles and our_style_id in our_style_ids:
+                if our_style_id not in self._current_preserved_styles:
+                    style_element = deepcopy(doc.styles.element.get_by_id(style_id))
+                    our_style_element = self.doc.styles.element.get_by_id(our_style_id)
+
+                    # Check if we already have an identical style
+                    preserved_style_ids = self._preserved_styles.get(
+                        our_style_id, [our_style_id]
+                    )
+                    matched_style_id = None
+                    for pstyle_id in preserved_style_ids:
+                        our_style_element = self.doc.styles.element.get_by_id(pstyle_id)
+                        if xml_elements_equal(
+                            style_element,
+                            our_style_element,
+                            ignored_tags=IGNORED_STYLE_TAGS,
+                        ):
+                            matched_style_id = pstyle_id
+                            self._current_preserved_styles[our_style_id] = (
+                                style_element.styleId
+                            )
+                            break
+                    # No matching style found, insert style with a new name
+                    if matched_style_id is None:
+                        new_id = increment_name(our_style_id)
+                        new_name = None
+                        if style_element.name is not None:
+                            new_name = increment_name(style_element.name.val)
+                        while new_id in our_style_ids:
+                            new_id = increment_name(new_id)
+                            if new_name is not None:
+                                new_name = increment_name(new_name)
+                        style_element.styleId = new_id
+                        if new_name is not None:
+                            style_element.name.val = new_name
+                        self.doc.styles.element.append(style_element)
+                        self.add_numberings(doc, style_element)
+                        self.add_linked_styles(doc, style_element)
+                        self._current_preserved_styles[our_style_id] = new_id
+                        self._preserved_styles.setdefault(
+                            our_style_id, [our_style_id]
+                        ).append(new_id)
+                    else:
+                        self._current_preserved_styles[our_style_id] = matched_style_id
+
+                for el in xpath(element, ".//w:tblStyle|.//w:pStyle|.//w:rStyle"):
+                    el.val = self._current_preserved_styles[our_style_id]
+            elif our_style_id not in our_style_ids:
                 style_element = deepcopy(doc.styles.element.get_by_id(style_id))
                 if style_element is not None:
                     self.doc.styles.element.append(style_element)
                     self.add_numberings(doc, style_element)
-                    # Also add linked styles
-                    linked_style_ids = xpath(style_element, ".//w:link/@w:val")
-                    if linked_style_ids:
-                        linked_style_id = linked_style_ids[0]
-                        our_linked_style_id = self.mapped_style_id(linked_style_id)
-                        if our_linked_style_id not in our_style_ids:
-                            our_linked_style = doc.styles.element.get_by_id(
-                                linked_style_id
-                            )
-                            if our_linked_style is not None:
-                                self.doc.styles.element.append(
-                                    deepcopy(our_linked_style)
-                                )
+                    self.add_linked_styles(doc, style_element)
             else:
                 # Create a mapping for abstractNumIds used in existing styles
                 # This is used when adding numberings to avoid having multiple
@@ -360,6 +409,17 @@ def add_styles(self, doc, element):
             # Update our style ids
             our_style_ids = [s.style_id for s in self.doc.styles]
 
+    def add_linked_styles(self, doc, element):
+        linked_style_ids = xpath(element, ".//w:link/@w:val")
+        if linked_style_ids:
+            linked_style_id = linked_style_ids[0]
+            our_linked_style_id = self.mapped_style_id(linked_style_id)
+            our_style_ids = [s.style_id for s in self.doc.styles]
+            if our_linked_style_id not in our_style_ids:
+                our_linked_style = doc.styles.element.get_by_id(linked_style_id)
+                if our_linked_style is not None:
+                    self.doc.styles.element.append(deepcopy(our_linked_style))
+
     def add_numberings(self, doc, element):
         """Add numberings from the given document used in the given element."""
         # Search for numbering references
diff --git a/docxcompose/server.py b/docxcompose/server.py
index 4a0a8cb..36885f4 100644
--- a/docxcompose/server.py
+++ b/docxcompose/server.py
@@ -10,6 +10,7 @@
 from docx import Document
 
 from docxcompose.composer import Composer
+from docxcompose.utils import to_bool
 
 
 CHUNK_SIZE = 65536
@@ -48,7 +49,7 @@ async def compose(request):
         composed_filename = os.path.join(temp_dir, "composed.docx")
 
         try:
-            composer = Composer(Document(documents.pop(0)))
+            composer = Composer(Document(documents.pop(0)), **compose_options(request))
             for document in documents:
                 composer.append(Document(document))
             composer.save(composed_filename)
@@ -63,6 +64,12 @@ async def compose(request):
         )
 
 
+def compose_options(request):
+    return {
+        "preserve_styles": to_bool(request.rel_url.query.get("preserve_styles", "")),
+    }
+
+
 async def save_part_to_file(part, directory):
     filename = os.path.join(directory, f"{part.name}_{part.filename}")
     with open(filename, "wb") as file_:
diff --git a/docxcompose/utils.py b/docxcompose/utils.py
index 36be83a..e287968 100644
--- a/docxcompose/utils.py
+++ b/docxcompose/utils.py
@@ -48,3 +48,87 @@ def word_to_python_date_format(format_str):
     for word_format, python_format in date_format_map:
         format_str = re.sub(word_format, python_format, format_str)
     return format_str
+
+
+def increment_name(name):
+    increment_part = name.split("_")[-1]
+    try:
+        increment = int(increment_part)
+    except ValueError:
+        return f"{name}_1"
+    return f"{name.removesuffix(increment_part)}{increment + 1}"
+
+
+def to_bool(value):
+    return value.lower() in ["1", "yes", "true", "on", "ok"]
+
+
+def xml_elements_equal(
+    left,
+    right,
+    ignored_tags=None,
+    compare_text=True,
+    compare_tail=False,
+    compare_attributes=True,
+):
+    return xml_element_signature(
+        left,
+        ignored_tags=ignored_tags,
+        compare_text=compare_text,
+        compare_tail=compare_tail,
+        compare_attributes=compare_attributes,
+    ) == xml_element_signature(
+        right,
+        ignored_tags=ignored_tags,
+        compare_text=compare_text,
+        compare_tail=compare_tail,
+        compare_attributes=compare_attributes,
+    )
+
+
+def xml_element_signature(
+    element,
+    ignored_tags=None,
+    compare_text=True,
+    compare_tail=False,
+    compare_attributes=True,
+    is_root=True,
+):
+    """
+    Creates a canonical, recursive representation of an element.
+
+    Child elements are included as a sorted list of signatures,
+    so their order is irrelevant.
+    """
+    tag = element.tag
+    attrs = tuple(sorted(element.attrib.items())) if compare_attributes else ()
+    text = normalize_text(element.text) if compare_text else None
+    tail = normalize_text(element.tail) if compare_tail else None
+
+    child_signatures = []
+    for child in element:
+        if ignored_tags and child.tag in ignored_tags:
+            continue
+
+        child_signatures.append(
+            xml_element_signature(
+                child,
+                ignored_tags=ignored_tags,
+                compare_text=compare_text,
+                compare_tail=compare_tail,
+                compare_attributes=compare_attributes,
+                is_root=False,
+            )
+        )
+    child_signatures.sort()
+
+    if is_root:
+        return (None, None, None, None, tuple(child_signatures))
+    else:
+        return (tag, attrs, text, tail, tuple(child_signatures))
+
+
+def normalize_text(value):
+    if value is None:
+        return ""
+    return value.strip()
diff --git a/tests/docs/composed_fixture/styles_preserve.docx b/tests/docs/composed_fixture/styles_preserve.docx
new file mode 100644
index 0000000..4845f7f
Binary files /dev/null and b/tests/docs/composed_fixture/styles_preserve.docx differ
diff --git a/tests/docs/styles_preserve1.docx b/tests/docs/styles_preserve1.docx
new file mode 100644
index 0000000..0329556
Binary files /dev/null and b/tests/docs/styles_preserve1.docx differ
diff --git a/tests/docs/styles_preserve2.docx b/tests/docs/styles_preserve2.docx
new file mode 100644
index 0000000..6da64a9
Binary files /dev/null and b/tests/docs/styles_preserve2.docx differ
diff --git a/tests/test_server.py b/tests/test_server.py
index 93f8360..91e3fbc 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -62,6 +62,18 @@ async def test_post_returns_500_if_compose_fails(http_client):
     assert text == "Failed composing documents"
 
 
+async def test_post_with_url_parameters(http_client):
+    files = {
+        "master": open(docx_path("master.docx"), "rb"),
+        "table": open(docx_path("table.docx"), "rb"),
+    }
+    resp = await http_client.post("/?preserve_styles=1", data=files)
+    assert resp.status == 200
+    composed_doc = ComparableDocument(Document(BytesIO(await resp.read())))
+    composed_fixture = FixtureDocument("table.docx")
+    assert composed_doc == composed_fixture
+
+
 async def test_healtcheck_returns_200(http_client):
     resp = await http_client.get("/healthcheck")
     assert resp.status == 200
diff --git a/tests/test_styles.py b/tests/test_styles.py
index 3b0060e..cc160d7 100644
--- a/tests/test_styles.py
+++ b/tests/test_styles.py
@@ -1,5 +1,6 @@
 import pytest
 from docx import Document
+from utils import ComparableDocument
 from utils import ComposedDocument
 from utils import docx_path
 from utils import FixtureDocument
@@ -64,6 +65,42 @@ def test_continue_when_no_styles():
     ComposedDocument("aatmay.docx", "aatmay.docx")
 
 
+def test_preserve_styles_with_same_id():
+    composer = Composer(
+        Document(docx_path("styles_preserve1.docx")), preserve_styles=True
+    )
+    composer.append(Document(docx_path("styles_preserve2.docx")))
+    style_ids = [s.style_id for s in composer.doc.styles]
+    assert "MyCustomStyle" in style_ids
+    assert "MyCustomStyle_1" in style_ids
+
+    expected = FixtureDocument("styles_preserve.docx")
+    composed = ComparableDocument(composer.doc)
+    assert composed == expected
+
+
+def test_ignore_styles_with_same_id():
+    composer = Composer(Document(docx_path("styles_preserve1.docx")))
+    composer.append(Document(docx_path("styles_preserve2.docx")))
+    style_ids = [s.style_id for s in composer.doc.styles]
+    assert "MyCustomStyle" in style_ids
+    assert "MyCustomStyle_1" not in style_ids
+
+
+def test_preserve_styles_does_not_duplicate_identical_styles():
+    composer = Composer(
+        Document(docx_path("styles_preserve1.docx")), preserve_styles=True
+    )
+    composer.append(Document(docx_path("styles_preserve2.docx")))
+    composer.append(Document(docx_path("styles_preserve2.docx")))
+    composer.append(Document(docx_path("styles_preserve1.docx")))
+    assert [
+        s.style_id
+        for s in composer.doc.styles
+        if s.style_id.startswith("MyCustomStyle")
+    ] == ["MyCustomStyle", "MyCustomStyleZchn", "MyCustomStyle_1"]
+
+
 @pytest.fixture
 def merged_styles():
     composer = Composer(Document(docx_path("styles_en.docx")))
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..8509578
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,43 @@
+from lxml import etree
+
+from docxcompose.utils import xml_elements_equal
+
+
+def test_xml_elements_are_equal():
+    xml1 = """
+    <root>
+        <a x="1">Foo</a>
+        <b>Bar</b>
+        <ignore_me>123</ignore_me>
+    </root>
+    """
+    xml2 = """
+    <root>
+        <b>Bar</b>
+        <a x="1">Foo</a>
+        <ignore_me>999</ignore_me>
+    </root>
+    """
+    e1 = etree.fromstring(xml1)
+    e2 = etree.fromstring(xml2)
+    assert xml_elements_equal(e1, e2, ignored_tags=["ignore_me"]) is True
+
+
+def test_xml_elements_are_not_equal():
+    xml1 = """
+    <root>
+        <a x="1">Foo</a>
+        <b>Bar</b>
+        <ignore_me>123</ignore_me>
+    </root>
+    """
+    xml2 = """
+    <root>
+        <b>Bar</b>
+        <a x="2">Foo</a>
+        <ignore_me>999</ignore_me>
+    </root>
+    """
+    e1 = etree.fromstring(xml1)
+    e2 = etree.fromstring(xml2)
+    assert xml_elements_equal(e1, e2, ignored_tags=["ignore_me"]) is False