diff --git a/src/blenderbim/blenderbim/core/document.py b/src/blenderbim/blenderbim/core/document.py
index ce6dc374c6..85cfc00681 100644
--- a/src/blenderbim/blenderbim/core/document.py
+++ b/src/blenderbim/blenderbim/core/document.py
@@ -109,7 +109,7 @@ def remove_document(ifc, document_tool, document=None):
 
 
 def assign_document(ifc, product=None, document=None):
-    ifc.run("document.assign_document", product=product, document=document)
+    ifc.run("document.assign_document", products=[product], document=document)
 
 
 def unassign_document(ifc, product=None, document=None):
diff --git a/src/blenderbim/blenderbim/core/drawing.py b/src/blenderbim/blenderbim/core/drawing.py
index f8039488f2..127cbfa7db 100644
--- a/src/blenderbim/blenderbim/core/drawing.py
+++ b/src/blenderbim/blenderbim/core/drawing.py
@@ -241,7 +241,7 @@ def add_drawing(ifc, collector, drawing, target_view=None, location_hint=None):
         attributes = {"Identification": "X", "Name": drawing_name, "Scope": "DRAWING"}
     ifc.run("document.edit_information", information=information, attributes=attributes)
     ifc.run("document.edit_reference", reference=reference, attributes={"Location": uri})
-    ifc.run("document.assign_document", product=element, document=reference)
+    ifc.run("document.assign_document", products=[element], document=reference)
     drawing.import_drawings()
 
 
@@ -276,7 +276,7 @@ def duplicate_drawing(ifc, drawing_tool, drawing=None, should_duplicate_annotati
         attributes = {"Identification": "X", "Name": drawing_name, "Scope": "DRAWING"}
     ifc.run("document.edit_information", information=information, attributes=attributes)
     ifc.run("document.edit_reference", reference=reference, attributes={"Location": uri})
-    ifc.run("document.assign_document", product=new_drawing, document=reference)
+    ifc.run("document.assign_document", products=[new_drawing], document=reference)
 
     drawing_tool.import_drawings()
     return new_drawing
diff --git a/src/blenderbim/test/core/test_document.py b/src/blenderbim/test/core/test_document.py
index 708c899e48..2349870d39 100644
--- a/src/blenderbim/test/core/test_document.py
+++ b/src/blenderbim/test/core/test_document.py
@@ -133,7 +133,7 @@ class TestRemoveDocument:
 
 class TestAssignDocument:
     def test_run(self, ifc):
-        ifc.run("document.assign_document", product="product", document="document").should_be_called()
+        ifc.run("document.assign_document", products=["product"], document="document").should_be_called()
         subject.assign_document(ifc, product="product", document="document")
 
 
diff --git a/src/blenderbim/test/core/test_drawing.py b/src/blenderbim/test/core/test_drawing.py
index b07d0f8368..afe116d072 100644
--- a/src/blenderbim/test/core/test_drawing.py
+++ b/src/blenderbim/test/core/test_drawing.py
@@ -365,7 +365,7 @@ class TestAddDrawing:
             attributes={"Identification": "X", "Name": "name", "Scope": "DRAWING"},
         ).should_be_called()
         ifc.run("document.edit_reference", reference="reference", attributes={"Location": "uri"}).should_be_called()
-        ifc.run("document.assign_document", product="element", document="reference").should_be_called()
+        ifc.run("document.assign_document", products=["element"], document="reference").should_be_called()
         drawing.import_drawings().should_be_called()
         subject.add_drawing(ifc, collector, drawing, target_view="target_view", location_hint="location_hint")
 
@@ -405,7 +405,7 @@ class TestDuplicateDrawing:
         ifc.run(
             "document.edit_reference", reference="reference", attributes={"Location": "drawing_path"}
         ).should_be_called()
-        ifc.run("document.assign_document", product="new_drawing", document="reference").should_be_called()
+        ifc.run("document.assign_document", products=["new_drawing"], document="reference").should_be_called()
 
         drawing.import_drawings().should_be_called()
         subject.duplicate_drawing(ifc, drawing, drawing="drawing", should_duplicate_annotations=True)
diff --git a/src/ifcopenshell-python/ifcopenshell/api/__init__.py b/src/ifcopenshell-python/ifcopenshell/api/__init__.py
index 6d27dbebfd..c82e076464 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/__init__.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/__init__.py
@@ -99,6 +99,9 @@ ARGUMENTS_DEPRECATION = {
     "library.unassign_reference": partial(
         batching_argument_deprecation, prev_argument="product", new_argument="products"
     ),
+    "document.assign_document": partial(
+        batching_argument_deprecation, prev_argument="product", new_argument="products"
+    ),
 }
 
 
diff --git a/src/ifcopenshell-python/ifcopenshell/api/document/assign_document.py b/src/ifcopenshell-python/ifcopenshell/api/document/assign_document.py
index c7f98e4517..f67cbe890a 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/document/assign_document.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/document/assign_document.py
@@ -17,11 +17,19 @@
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
 import ifcopenshell
+import ifcopenshell.api
+import ifcopenshell.util.element
+from typing import Union
 
 
 class Usecase:
-    def __init__(self, file, product=None, document=None):
-        """Assigns a document to a product
+    def __init__(
+        self,
+        file: ifcopenshell.file,
+        products: list[ifcopenshell.entity_instance],
+        document: ifcopenshell.entity_instance,
+    ):
+        """Assigns a document to a list of products
 
         An object may be assigned to zero, one, or multiple documents. Almost
         any object or property may be assigned to a document, though typically
@@ -32,14 +40,16 @@ class Usecase:
         consistent with other external relationships (such as classification
         systems or libraries).
 
-        :param product: The object to associate the document to. This could be
+        :param product: The list of objects to associate the document to. This could be
             almost any sensible object in IFC.
-        :type product: ifcopenshell.entity_instance.entity_instance
+        :type product: list[ifcopenshell.entity_instance.entity_instance]
         :param document: The IfcDocumentReference to associate to, or
             alternatively an IfcDocumentInformation, though this is not
             recommended.
         :type document: ifcopenshell.entity_instance.entity_instance
         :return: The IfcRelAssociatesDocument relationship
+            or `None` if `products` was an empty list or all products were
+            already assigned to the `document`.
         :rtype: ifcopenshell.entity_instance.entity_instance
 
         Example:
@@ -54,42 +64,51 @@ class Usecase:
             reference = ifcopenshell.api.run("document.add_reference", model, information=document)
 
             # Let's imagine storey represents an IfcBuildingStorey for the ground floor
-            ifcopenshell.api.run("document.assign_document", model, product=storey, document=reference)
+            ifcopenshell.api.run("document.assign_document", model, products=[storey], document=reference)
         """
         self.file = file
         self.settings = {
-            "product": product,
+            "products": products,
             "document": document,
         }
 
-    def execute(self):
-        rel = self.get_document_rel()
-        related_objects = set(rel.RelatedObjects) if rel.RelatedObjects else set()
-        related_objects.add(self.settings["product"])
-        rel.RelatedObjects = list(related_objects)
+    def execute(self) -> Union[ifcopenshell.entity_instance, None]:
+        # TODO: do we need to support non-ifcroot elements like we do in classification.add_reference?
+        # NOTE: reuses code from `library.assign_reference`
+
+        referenced_elements = ifcopenshell.util.element.get_referenced_elements(self.settings["document"])
+        products: set[ifcopenshell.entity_instance] = set(self.settings["products"])
+        products = products - referenced_elements
+
+        if not products:
+            return
 
-    def get_document_rel(self):
         if self.file.schema == "IFC2X3":
-            for rel in self.file.by_type("IfcRelAssociatesDocument"):
-                if rel.RelatingDocument == self.settings["document"]:
-                    return rel
+            rel = next(
+                (
+                    r
+                    for r in self.file.by_type("IfcRelAssociatesDocument")
+                    if r.RelatingDocument == self.settings["document"]
+                ),
+                None,
+            )
         else:
-            if (
-                hasattr(self.settings["document"], "DocumentRefForObjects")
-                and self.settings["document"].DocumentRefForObjects
-            ):
-                return self.settings["document"].DocumentRefForObjects[0]
-            elif (
-                hasattr(self.settings["document"], "DocumentInfoForObjects")
-                and self.settings["document"].DocumentInfoForObjects
-            ):
-                return self.settings["document"].DocumentInfoForObjects[0]
+            ifc_class = self.settings["document"].is_a()
+            if ifc_class == "IfcDocumentReference":
+                rel = next(iter(self.settings["document"].DocumentRefForObjects), None)
+            elif ifc_class == "IfcDocumentInformation":
+                rel = next(iter(self.settings["document"].DocumentInfoForObjects), None)
 
-        return self.file.create_entity(
-            "IfcRelAssociatesDocument",
-            **{
-                "GlobalId": ifcopenshell.guid.new(),
-                "OwnerHistory": ifcopenshell.api.run("owner.create_owner_history", self.file),
-                "RelatingDocument": self.settings["document"],
-            }
-        )
+        if not rel:
+            return self.file.create_entity(
+                "IfcRelAssociatesDocument",
+                GlobalId=ifcopenshell.guid.new(),
+                OwnerHistory=ifcopenshell.api.run("owner.create_owner_history", self.file),
+                RelatedObjects=list(products),
+                RelatingDocument=self.settings["document"],
+            )
+
+        related_objects = set(rel.RelatedObjects) | products
+        rel.RelatedObjects = list(related_objects)
+        ifcopenshell.api.run("owner.update_owner_history", self.file, element=rel)
+        return rel
diff --git a/src/ifcopenshell-python/ifcopenshell/api/document/unassign_document.py b/src/ifcopenshell-python/ifcopenshell/api/document/unassign_document.py
index 5a08c13262..c4fbca8234 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/document/unassign_document.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/document/unassign_document.py
@@ -45,7 +45,7 @@ class Usecase:
             reference = ifcopenshell.api.run("document.add_reference", model, information=document)
 
             # Let's imagine storey represents an IfcBuildingStorey for the ground floor
-            ifcopenshell.api.run("document.assign_document", model, product=storey, document=reference)
+            ifcopenshell.api.run("document.assign_document", model, products=[storey], document=reference)
 
             # Now let's change our mind and remove the association
             ifcopenshell.api.run("document.unassign_document", model, product=storey, document=reference)
diff --git a/src/ifcopenshell-python/test/api/document/test_assign_document.py b/src/ifcopenshell-python/test/api/document/test_assign_document.py
index 6c76f844b4..32d584ac51 100644
--- a/src/ifcopenshell-python/test/api/document/test_assign_document.py
+++ b/src/ifcopenshell-python/test/api/document/test_assign_document.py
@@ -18,22 +18,25 @@
 
 import test.bootstrap
 import ifcopenshell.api
+import ifcopenshell.util.element
 
 
 class TestAssignDocument(test.bootstrap.IFC4):
     def test_assigning_a_document(self):
         element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         reference = ifcopenshell.api.run("document.add_reference", self.file, information=None)
-        ifcopenshell.api.run("document.assign_document", self.file, product=element, document=reference)
+        ifcopenshell.api.run("document.assign_document", self.file, products=[element], document=reference)
         assert element.HasAssociations[0].RelatingDocument == reference
+        assert ifcopenshell.util.element.get_referenced_elements(reference) == {element}
 
     def test_assigning_multiple_documents(self):
         element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         element2 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         reference = ifcopenshell.api.run("document.add_reference", self.file, information=None)
-        ifcopenshell.api.run("document.assign_document", self.file, product=element, document=reference)
-        ifcopenshell.api.run("document.assign_document", self.file, product=element2, document=reference)
+        ifcopenshell.api.run("document.assign_document", self.file, products=[element, element2], document=reference)
         assert len(self.file.by_type("IfcRelAssociatesDocument")) == 1
-        assert element.HasAssociations[0].RelatingDocument == reference
-        assert element2.HasAssociations[0].RelatingDocument == reference
-        assert element.HasAssociations[0] == element.HasAssociations[0]
+        assert ifcopenshell.util.element.get_referenced_elements(reference) == {element, element2}
+
+
+class TestAssignDocumentIFC2X3(test.bootstrap.IFC2X3, TestAssignDocument):
+    pass
diff --git a/src/ifcopenshell-python/test/api/document/test_remove_reference.py b/src/ifcopenshell-python/test/api/document/test_remove_reference.py
index e5f5892172..a1b3c260e2 100644
--- a/src/ifcopenshell-python/test/api/document/test_remove_reference.py
+++ b/src/ifcopenshell-python/test/api/document/test_remove_reference.py
@@ -35,7 +35,7 @@ class TestRemoveReference(test.bootstrap.IFC4):
         wall = self.file.createIfcWall()
         information = ifcopenshell.api.run("document.add_information", self.file, parent=None)
         reference = ifcopenshell.api.run("document.add_reference", self.file, information=information)
-        ifcopenshell.api.run("document.assign_document", self.file, product=wall, document=reference)
+        ifcopenshell.api.run("document.assign_document", self.file, products=[wall], document=reference)
         assert len(self.file.by_type("IfcRelAssociatesDocument")) == 2
         ifcopenshell.api.run("document.remove_reference", self.file, reference=reference)
         assert len(self.file.by_type("IfcDocumentReference")) == 0
diff --git a/src/ifcopenshell-python/test/api/document/test_unassign_document.py b/src/ifcopenshell-python/test/api/document/test_unassign_document.py
index 8f227dd2b2..f58975ce69 100644
--- a/src/ifcopenshell-python/test/api/document/test_unassign_document.py
+++ b/src/ifcopenshell-python/test/api/document/test_unassign_document.py
@@ -24,7 +24,7 @@ class TestUnassignDocument(test.bootstrap.IFC4):
     def test_unassigning_a_document(self):
         element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         reference = ifcopenshell.api.run("document.add_reference", self.file, information=None)
-        ifcopenshell.api.run("document.assign_document", self.file, product=element, document=reference)
+        ifcopenshell.api.run("document.assign_document", self.file, products=[element], document=reference)
         ifcopenshell.api.run("document.unassign_document", self.file, product=element, document=reference)
         assert not element.HasAssociations
         assert not len(self.file.by_type("IfcRelAssociatesDocument"))
@@ -33,8 +33,8 @@ class TestUnassignDocument(test.bootstrap.IFC4):
         element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         element2 = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
         reference = ifcopenshell.api.run("document.add_reference", self.file, information=None)
-        ifcopenshell.api.run("document.assign_document", self.file, product=element, document=reference)
-        ifcopenshell.api.run("document.assign_document", self.file, product=element2, document=reference)
+        ifcopenshell.api.run("document.assign_document", self.file, products=[element], document=reference)
+        ifcopenshell.api.run("document.assign_document", self.file, products=[element2], document=reference)
         ifcopenshell.api.run("document.unassign_document", self.file, product=element, document=reference)
         assert not element.HasAssociations
         assert element2.HasAssociations[0].RelatingDocument == reference
diff --git a/src/ifcopenshell-python/test/api/test_api.py b/src/ifcopenshell-python/test/api/test_api.py
index a652a0de0c..66afb798a6 100644
--- a/src/ifcopenshell-python/test/api/test_api.py
+++ b/src/ifcopenshell-python/test/api/test_api.py
@@ -254,3 +254,10 @@ class TestTemporarySupportForDeprecatedAPIArguments(test.bootstrap.IFC4):
         ifcopenshell.api.run("library.assign_reference", self.file, products=[product], reference=reference)
         ifcopenshell.api.run("library.unassign_reference", self.file, product=product, reference=reference)
         assert len(self.file.by_type("IfcRelAssociatesLibrary")) == 0
+
+    @deprecation_check
+    def test_assigning_a_document(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        reference = ifcopenshell.api.run("document.add_reference", self.file, information=None)
+        ifcopenshell.api.run("document.assign_document", self.file, product=element, document=reference)
+        assert element.HasAssociations[0].RelatingDocument == reference
diff --git a/src/ifcopenshell-python/test/util/test_element.py b/src/ifcopenshell-python/test/util/test_element.py
index 1a701f5ec9..97363f8017 100644
--- a/src/ifcopenshell-python/test/util/test_element.py
+++ b/src/ifcopenshell-python/test/util/test_element.py
@@ -787,7 +787,6 @@ class TestGetNestIFC2X3(test.bootstrap.IFC2X3, TestGetNestIFC4):
 
 class TestGetReferencedElements(test.bootstrap.IFC4):
     # TODO: test other references:
-    # IfcDocumentReference
     # IfcExternallyDefinedHatchStyle
     # IfcExternallyDefinedSurfaceStyle
     # IfcExternallyDefinedTextFont
@@ -816,6 +815,15 @@ class TestGetReferencedElements(test.bootstrap.IFC4):
         ifcopenshell.api.run("library.assign_reference", self.file, reference=reference, products=elements)
         assert subject.get_referenced_elements(reference) == set(elements)
 
+    def test_get_elements_referenced_by_document_reference(self):
+        reference = ifcopenshell.api.run("document.add_reference", self.file, information=None)
+        elements = [
+            ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall"),
+            ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall"),
+        ]
+        ifcopenshell.api.run("document.assign_document", self.file, document=reference, products=elements)
+        assert subject.get_referenced_elements(reference) == set(elements)
+
 
 class TestGetReferencedElementsIFC2X3(test.bootstrap.IFC2X3, TestGetReferencedElements):
     pass