diff --git a/server/README.md b/server/README.md
index 1a3e42173..7a2a76ad5 100644
--- a/server/README.md
+++ b/server/README.md
@@ -109,22 +109,20 @@ The server can be accessed at http://localhost:8080/api/v3.1/ from your host sys
 ## Currently Unimplemented
 Several features and routes are currently not supported:
 
-1. Correlation ID: Not implemented because it was deemed unnecessary for this server.
+- Correlation ID: Not implemented because it was deemed unnecessary for this server.
 
-2. Extent Parameter (`withBlobValue/withoutBlobValue`):
+- Extent Parameter (`withBlobValue/withoutBlobValue`):
    Not implemented due to the lack of support in JSON/XML serialization.
 
-3. Route `/shells/{aasIdentifier}/asset-information/thumbnail`: Not implemented because the specification lacks clarity.
-
-4. Serialization and Description Routes:
+- Serialization and Description Routes:
    - `/serialization`
    - `/description`
    These routes are not implemented at this time.
 
-5. Value, Path, and PATCH Routes:
+- Value, Path, and PATCH Routes:
    - All `/…/value$`, `/…/path$`, and `PATCH` routes are currently not implemented.
 
-6. Operation Invocation Routes: The following routes are not implemented because operation invocation
+- Operation Invocation Routes: The following routes are not implemented because operation invocation
    is not yet supported by the `basyx-python-sdk`:
    - `POST /submodels/{submodelIdentifier}/submodel-elements/{idShortPath}/invoke`
    - `POST /submodels/{submodelIdentifier}/submodel-elements/{idShortPath}/invoke/$value`
diff --git a/server/app/interfaces/repository.py b/server/app/interfaces/repository.py
index 8f931c786..551125835 100644
--- a/server/app/interfaces/repository.py
+++ b/server/app/interfaces/repository.py
@@ -79,8 +79,18 @@ def __init__(
                                         ),
                                         Rule(
                                             "/asset-information/thumbnail",
-                                            methods=["GET", "PUT", "DELETE"],
-                                            endpoint=self.not_implemented,
+                                            methods=["GET"],
+                                            endpoint=self.get_aas_thumbnail,
+                                        ),
+                                        Rule(
+                                            "/asset-information/thumbnail",
+                                            methods=["PUT"],
+                                            endpoint=self.put_aas_thumbnail,
+                                        ),
+                                        Rule(
+                                            "/asset-information/thumbnail",
+                                            methods=["DELETE"],
+                                            endpoint=self.delete_aas_thumbnail,
                                         ),
                                         Rule("/submodel-refs", methods=["GET"], endpoint=self.get_aas_submodel_refs),
                                         Rule("/submodel-refs", methods=["POST"], endpoint=self.post_aas_submodel_refs),
@@ -586,6 +596,66 @@ def put_aas_asset_information(
         self.object_store.commit(aas)
         return response_t()
 
+    def get_aas_thumbnail(
+        self, request: Request, url_args: Dict, response_t: Type[APIResponse], **_kwargs
+    ) -> Response:
+        shell = self._get_shell(url_args)
+        thumbnail = shell.asset_information.default_thumbnail
+        if thumbnail is None or not thumbnail.path:
+            raise NotFound(f"{shell!r} has no default thumbnail set!")
+        if not thumbnail.path.startswith("/"):
+            raise BadRequest(f"{shell!r} references an external thumbnail: {thumbnail.path}")
+        bytes_io = io.BytesIO()
+        try:
+            self.file_store.write_file(thumbnail.path, bytes_io)
+        except KeyError:
+            raise NotFound(f"No thumbnail file found at path: {thumbnail.path}")
+        return Response(bytes_io.getvalue(), content_type=thumbnail.content_type or "application/octet-stream")
+
+    def put_aas_thumbnail(
+        self, request: Request, url_args: Dict, response_t: Type[APIResponse], **_kwargs
+    ) -> Response:
+        shell = self._get_shell(url_args)
+        filename = request.form.get("fileName")
+        if filename is None:
+            raise BadRequest("No 'fileName' specified!")
+        elif not filename.startswith("/"):
+            raise BadRequest(f"Given 'fileName' doesn't start with a slash (/): {filename}")
+
+        file_storage: Optional[FileStorage] = request.files.get("file")
+        if file_storage is None:
+            raise BadRequest("Missing file to upload")
+
+        old_thumbnail = shell.asset_information.default_thumbnail
+        new_path = self.file_store.add_file(filename, file_storage.stream, file_storage.mimetype)
+        if old_thumbnail is not None and old_thumbnail.path and old_thumbnail.path.startswith("/") \
+                and old_thumbnail.path != new_path:
+            try:
+                self.file_store.delete_file(old_thumbnail.path)
+            except KeyError:
+                pass
+
+        shell.asset_information.default_thumbnail = model.Resource(new_path, file_storage.mimetype)
+        self.object_store.commit(shell)
+        return response_t()
+
+    def delete_aas_thumbnail(
+        self, request: Request, url_args: Dict, response_t: Type[APIResponse], **_kwargs
+    ) -> Response:
+        shell = self._get_shell(url_args)
+        thumbnail = shell.asset_information.default_thumbnail
+        if thumbnail is None or not thumbnail.path:
+            raise NotFound(f"{shell!r} has no default thumbnail set!")
+        if not thumbnail.path.startswith("/"):
+            raise BadRequest(f"{shell!r} references an external thumbnail: {thumbnail.path}")
+        try:
+            self.file_store.delete_file(thumbnail.path)
+        except KeyError:
+            pass
+        shell.asset_information.default_thumbnail = None
+        self.object_store.commit(shell)
+        return response_t()
+
     def get_aas_submodel_refs(
         self, request: Request, url_args: Dict, response_t: Type[APIResponse], **_kwargs
     ) -> Response: