diff --git a/CHANGELOG.md b/CHANGELOG.md
index 24d0e6fd1..5c6fd3590 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - `STAC_INDEX_ASSETS` environment variable to allow asset serialization to be configurable. [#433](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/433)
 - Added the `ENV_MAX_LIMIT` environment variable to SFEOS, allowing overriding of the `MAX_LIMIT`, which controls the `?limit` parameter for returned items and STAC collections. [#434](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/434)
 - Sort, Query, and Filter extension and functionality to the item collection route. [#437](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/437)
+- Added Fields Extension implementation for the `/collections/{collection_id}/items` endpoint. [#436](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/436)
 
 ### Changed
 
diff --git a/stac_fastapi/core/stac_fastapi/core/core.py b/stac_fastapi/core/stac_fastapi/core/core.py
index 7b4502669..627b02736 100644
--- a/stac_fastapi/core/stac_fastapi/core/core.py
+++ b/stac_fastapi/core/stac_fastapi/core/core.py
@@ -293,6 +293,7 @@ async def item_collection(
         filter_lang: Optional[str] = None,
         token: Optional[str] = None,
         query: Optional[str] = None,
+        fields: Optional[List[str]] = None,
         **kwargs,
     ) -> stac_types.ItemCollection:
         """List items within a specific collection.
@@ -314,6 +315,7 @@ async def item_collection(
             query (Optional[str]): Optional query string.
             filter_expr (Optional[str]): Optional filter expression.
             filter_lang (Optional[str]): Optional filter language.
+            fields (Optional[List[str]]): Fields to include or exclude from the results.
 
         Returns:
             ItemCollection: Feature collection with items, paging links, and counts.
@@ -338,6 +340,7 @@ async def item_collection(
             query=query,
             filter_expr=filter_expr,
             filter_lang=filter_lang,
+            fields=fields,
         )
 
     async def get_item(
diff --git a/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/app.py b/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/app.py
index 34c582c19..d83dc9f58 100644
--- a/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/app.py
+++ b/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/app.py
@@ -43,6 +43,7 @@
     TokenPaginationExtension,
     TransactionExtension,
 )
+from stac_fastapi.extensions.core.fields import FieldsConformanceClasses
 from stac_fastapi.extensions.core.filter import FilterConformanceClasses
 from stac_fastapi.extensions.core.query import QueryConformanceClasses
 from stac_fastapi.extensions.core.sort import SortConformanceClasses
@@ -85,8 +86,11 @@
 aggregation_extension.POST = EsAggregationExtensionPostRequest
 aggregation_extension.GET = EsAggregationExtensionGetRequest
 
+fields_extension = FieldsExtension()
+fields_extension.conformance_classes.append(FieldsConformanceClasses.ITEMS)
+
 search_extensions = [
-    FieldsExtension(),
+    fields_extension,
     QueryExtension(),
     SortExtension(),
     TokenPaginationExtension(),
@@ -133,6 +137,7 @@
             conformance_classes=[QueryConformanceClasses.ITEMS],
         ),
         filter_extension,
+        FieldsExtension(conformance_classes=[FieldsConformanceClasses.ITEMS]),
     ],
     request_type="GET",
 )
diff --git a/stac_fastapi/opensearch/stac_fastapi/opensearch/app.py b/stac_fastapi/opensearch/stac_fastapi/opensearch/app.py
index 26b4bc0ca..156558f02 100644
--- a/stac_fastapi/opensearch/stac_fastapi/opensearch/app.py
+++ b/stac_fastapi/opensearch/stac_fastapi/opensearch/app.py
@@ -37,6 +37,7 @@
     TokenPaginationExtension,
     TransactionExtension,
 )
+from stac_fastapi.extensions.core.fields import FieldsConformanceClasses
 from stac_fastapi.extensions.core.filter import FilterConformanceClasses
 from stac_fastapi.extensions.core.query import QueryConformanceClasses
 from stac_fastapi.extensions.core.sort import SortConformanceClasses
@@ -84,8 +85,11 @@
 aggregation_extension.POST = EsAggregationExtensionPostRequest
 aggregation_extension.GET = EsAggregationExtensionGetRequest
 
+fields_extension = FieldsExtension()
+fields_extension.conformance_classes.append(FieldsConformanceClasses.ITEMS)
+
 search_extensions = [
-    FieldsExtension(),
+    fields_extension,
     QueryExtension(),
     SortExtension(),
     TokenPaginationExtension(),
@@ -133,6 +137,7 @@
             conformance_classes=[QueryConformanceClasses.ITEMS],
         ),
         filter_extension,
+        FieldsExtension(conformance_classes=[FieldsConformanceClasses.ITEMS]),
     ],
     request_type="GET",
 )
diff --git a/stac_fastapi/tests/api/test_api_item_collection.py b/stac_fastapi/tests/api/test_api_item_collection.py
index 7c7b51b6f..2b1aa8e79 100644
--- a/stac_fastapi/tests/api/test_api_item_collection.py
+++ b/stac_fastapi/tests/api/test_api_item_collection.py
@@ -190,3 +190,71 @@ async def test_item_collection_filter_by_nonexistent_id(app_client, ctx, txn_cli
     assert (
         len(resp_json["features"]) == 0
     ), f"Expected no items with ID {non_existent_id}, but found {len(resp_json['features'])} matches"
+
+
+@pytest.mark.asyncio
+async def test_item_collection_fields_extension(app_client, ctx, txn_client):
+    resp = await app_client.get(
+        "/collections/test-collection/items",
+        params={"fields": "+properties.datetime"},
+    )
+    assert resp.status_code == 200
+    resp_json = resp.json()
+    assert list(resp_json["features"][0]["properties"]) == ["datetime"]
+
+
+@pytest.mark.asyncio
+async def test_item_collection_fields_extension_no_properties_get(
+    app_client, ctx, txn_client
+):
+    resp = await app_client.get(
+        "/collections/test-collection/items", params={"fields": "-properties"}
+    )
+    assert resp.status_code == 200
+    resp_json = resp.json()
+    assert "properties" not in resp_json["features"][0]
+
+
+@pytest.mark.asyncio
+async def test_item_collection_fields_extension_no_null_fields(
+    app_client, ctx, txn_client
+):
+    resp = await app_client.get("/collections/test-collection/items")
+    assert resp.status_code == 200
+    resp_json = resp.json()
+    # check if no null fields: https://github.com/stac-utils/stac-fastapi-elasticsearch/issues/166
+    for feature in resp_json["features"]:
+        # assert "bbox" not in feature["geometry"]
+        for link in feature["links"]:
+            assert all(a not in link or link[a] is not None for a in ("title", "asset"))
+        for asset in feature["assets"]:
+            assert all(
+                a not in asset or asset[a] is not None
+                for a in ("start_datetime", "created")
+            )
+
+
+@pytest.mark.asyncio
+async def test_item_collection_fields_extension_return_all_properties(
+    app_client, ctx, txn_client, load_test_data
+):
+    item = load_test_data("test_item.json")
+    resp = await app_client.get(
+        "/collections/test-collection/items",
+        params={"collections": ["test-collection"], "fields": "properties"},
+    )
+    assert resp.status_code == 200
+    resp_json = resp.json()
+    feature = resp_json["features"][0]
+    assert len(feature["properties"]) >= len(item["properties"])
+    for expected_prop, expected_value in item["properties"].items():
+        if expected_prop in (
+            "datetime",
+            "start_datetime",
+            "end_datetime",
+            "created",
+            "updated",
+        ):
+            assert feature["properties"][expected_prop][0:19] == expected_value[0:19]
+        else:
+            assert feature["properties"][expected_prop] == expected_value
diff --git a/stac_fastapi/tests/conftest.py b/stac_fastapi/tests/conftest.py
index 23da26687..08e3277dc 100644
--- a/stac_fastapi/tests/conftest.py
+++ b/stac_fastapi/tests/conftest.py
@@ -362,8 +362,8 @@ def build_test_app():
     aggregation_extension.GET = EsAggregationExtensionGetRequest
 
     search_extensions = [
-        SortExtension(),
         FieldsExtension(),
+        SortExtension(),
         QueryExtension(),
         TokenPaginationExtension(),
         FilterExtension(),
diff --git a/stac_fastapi/tests/resources/test_item.py b/stac_fastapi/tests/resources/test_item.py
index 0299cdc00..7ba563df8 100644
--- a/stac_fastapi/tests/resources/test_item.py
+++ b/stac_fastapi/tests/resources/test_item.py
@@ -869,6 +869,35 @@ async def test_field_extension_exclude_default_includes(app_client, ctx):
     assert "gsd" not in resp_json["features"][0]
 
 
+@pytest.mark.asyncio
+async def test_field_extension_get_includes_collection_items(app_client, ctx):
+    """Test GET collections/{collection_id}/items with included fields (fields extension)"""
+    test_item = ctx.item
+    params = {
+        "fields": "+properties.proj:epsg,+properties.gsd",
+    }
+    resp = await app_client.get(
+        f"/collections/{test_item['collection']}/items", params=params
+    )
+    feat_properties = resp.json()["features"][0]["properties"]
+    assert not set(feat_properties) - {"proj:epsg", "gsd", "datetime"}
+
+
+@pytest.mark.asyncio
+async def test_field_extension_get_excludes_collection_items(app_client, ctx):
+    """Test GET collections/{collection_id}/items with included fields (fields extension)"""
+    test_item = ctx.item
+    params = {
+        "fields": "-properties.proj:epsg,-properties.gsd",
+    }
+    resp = await app_client.get(
+        f"/collections/{test_item['collection']}/items", params=params
+    )
+    resp_json = resp.json()
+    assert "proj:epsg" not in resp_json["features"][0]["properties"].keys()
+    assert "gsd" not in resp_json["features"][0]["properties"].keys()
+
+
 @pytest.mark.asyncio
 async def test_search_intersects_and_bbox(app_client):
     """Test POST search intersects and bbox are mutually exclusive (core)"""