diff --git a/CHANGES.md b/CHANGES.md
index 940b7b844..a41037637 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -6,6 +6,7 @@
 
 * switch from `fastapi` to `fastapi-slim` to avoid installing unwanted dependencies. ([#687](https://github.com/stac-utils/stac-fastapi/pull/687))
 * replace Enum with `Literal` for `FilterLang`. ([#686](https://github.com/stac-utils/stac-fastapi/pull/686))
+* Added `collection-search` extension
 
 ### Removed
 
diff --git a/stac_fastapi/api/stac_fastapi/api/config.py b/stac_fastapi/api/stac_fastapi/api/config.py
index 3918421ff..81b148293 100644
--- a/stac_fastapi/api/stac_fastapi/api/config.py
+++ b/stac_fastapi/api/stac_fastapi/api/config.py
@@ -18,6 +18,7 @@ class ApiExtensions(enum.Enum):
     query = "query"
     sort = "sort"
     transaction = "transaction"
+    collection_search = "collection-search"
 
 
 class AddOns(enum.Enum):
diff --git a/stac_fastapi/extensions/stac_fastapi/extensions/core/__init__.py b/stac_fastapi/extensions/stac_fastapi/extensions/core/__init__.py
index 74f15ed0a..be608101c 100644
--- a/stac_fastapi/extensions/stac_fastapi/extensions/core/__init__.py
+++ b/stac_fastapi/extensions/stac_fastapi/extensions/core/__init__.py
@@ -1,5 +1,4 @@
 """stac_api.extensions.core module."""
-
 from .context import ContextExtension
 from .fields import FieldsExtension
 from .filter import FilterExtension
@@ -7,6 +6,7 @@
 from .query import QueryExtension
 from .sort import SortExtension
 from .transaction import TransactionExtension
+from .collectionSearch import CollectionSearchExtension
 
 __all__ = (
     "ContextExtension",
@@ -17,4 +17,5 @@
     "SortExtension",
     "TokenPaginationExtension",
     "TransactionExtension",
+    "CollectionSearchExtension",
 )
diff --git a/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/__init__.py b/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/__init__.py
new file mode 100644
index 000000000..21f35e8ca
--- /dev/null
+++ b/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/__init__.py
@@ -0,0 +1,6 @@
+"""Filter extension module."""
+
+
+from .collectionSearch import CollectionSearchExtension
+
+__all__ = ["CollectionSearchExtension"]
diff --git a/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/collectionSearch.py b/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/collectionSearch.py
new file mode 100644
index 000000000..39723fb26
--- /dev/null
+++ b/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/collectionSearch.py
@@ -0,0 +1,124 @@
+# encoding: utf-8
+"""Collection Search Extension."""
+from enum import Enum
+from typing import List, Type, Union
+
+import attr
+from fastapi import APIRouter, FastAPI
+from stac_pydantic.api.collections import Collections
+from starlette.responses import Response
+
+from stac_fastapi.api.models import JSONSchemaResponse
+from stac_fastapi.api.routes import create_async_endpoint
+from stac_fastapi.types.config import ApiSettings
+from stac_fastapi.types.core import (
+    AsyncBaseCollectionSearchClient,
+    BaseCollectionSearchClient,
+)
+from stac_fastapi.types.extension import ApiExtension
+from stac_fastapi.types.search import (
+    BaseCollectionSearchGetRequest,
+    BaseCollectionSearchPostRequest,
+)
+
+from .request import (
+    CollectionSearchExtensionGetRequest,
+    CollectionSearchExtensionPostRequest,
+)
+
+
+class CollectionSearchConformanceClasses(str, Enum):
+    """Conformance classes for the Collection Search extension.
+
+    See
+    https://github.com/stac-api-extensions/collection-search
+    """
+
+    CORE = "https://api.stacspec.org/v1.0.0-rc.1/core"
+    COLLECTION_SEARCH = "https://api.stacspec.org/v1.0.0-rc.1/collection-search"
+    SIMPLE_QUERY = "http://www.opengis.net/spec/ogcapi-common-2/1.0/conf/simple-query"
+
+
+@attr.s
+class CollectionSearchExtension(ApiExtension):
+    """CollectionSearch Extension.
+
+    The collection search extension adds two endpoints which allow searching of
+    collections via GET and POST, to avoid conflict with /collections endpoints
+    those used here are:
+        GET /collection-search
+        POST /collection-search
+
+    https://github.com/stac-api-extensions/collection-search
+
+    Attributes:
+        search_get_request_model: Get request model for collection search
+        search_post_request_model: Post request model for collection search
+        client: Collection Search endpoint logic
+        conformance_classes: Conformance classes provided by the extension
+    """
+
+    GET = CollectionSearchExtensionGetRequest
+    POST = CollectionSearchExtensionPostRequest
+
+    client: Union[AsyncBaseCollectionSearchClient, BaseCollectionSearchClient] = attr.ib(
+        factory=BaseCollectionSearchClient
+    )
+    settings: ApiSettings = attr.ib(default=ApiSettings())
+
+    collection_search_get_request_model: Type[BaseCollectionSearchGetRequest] = attr.ib(
+        default=BaseCollectionSearchGetRequest
+    )
+    collection_search_post_request_model: Type[BaseCollectionSearchPostRequest] = attr.ib(
+        default=BaseCollectionSearchPostRequest
+    )
+
+    conformance_classes: List[str] = attr.ib(
+        default=[
+            CollectionSearchConformanceClasses.CORE,
+            CollectionSearchConformanceClasses.COLLECTION_SEARCH,
+            CollectionSearchConformanceClasses.SIMPLE_QUERY,
+        ]
+    )
+    router: APIRouter = attr.ib(factory=APIRouter)
+    response_class: Type[Response] = attr.ib(default=JSONSchemaResponse)
+
+    def register(self, app: FastAPI) -> None:
+        """Register the extension with a FastAPI application.
+
+        Args:
+            app: target FastAPI application.
+
+        Returns:
+            None
+        """
+        self.router.prefix = app.state.router_prefix
+        self.router.add_api_route(
+            name="Collection Search",
+            path="/collection-search",
+            response_model=Collections if self.settings.enable_response_models else None,
+            response_class=self.response_class,
+            response_model_exclude_unset=True,
+            response_model_exclude_none=True,
+            methods=["GET"],
+            endpoint=create_async_endpoint(
+                self.client.get_collection_search,
+                self.collection_search_get_request_model,
+            ),
+        )
+
+        self.router.add_api_route(
+            name="Collection Search",
+            path="/collection-search",
+            response_model=Collections if self.settings.enable_response_models else None,
+            response_class=self.response_class,
+            response_model_exclude_unset=True,
+            response_model_exclude_none=True,
+            methods=["POST"],
+            endpoint=create_async_endpoint(
+                self.client.post_collection_search,
+                self.collection_search_post_request_model,
+            ),
+        )
+
+        app.include_router(self.router, tags=["Collection Search Extension"])
diff --git a/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/request.py b/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/request.py
new file mode 100644
index 000000000..f159d6a87
--- /dev/null
+++ b/stac_fastapi/extensions/stac_fastapi/extensions/core/collectionSearch/request.py
@@ -0,0 +1,28 @@
+"""Collection Search extension request models."""
+
+from enum import Enum
+from typing import Any, Dict, Optional, List
+
+import attr
+from pydantic import BaseModel, Field
+from stac_pydantic.shared import BBox
+
+from stac_fastapi.types.search import APIRequest, Limit, str2bbox
+
+from stac_fastapi.types.rfc3339 import DateTimeType, str_to_interval
+
+@attr.s
+class CollectionSearchExtensionGetRequest(APIRequest):
+    """Collection Search extension GET request model."""
+
+    bbox: Optional[BBox] = attr.ib(default=None, converter=str2bbox)
+    datetime: Optional[DateTimeType] = attr.ib(default=None, converter=str_to_interval)
+    limit: Optional[int] = attr.ib(default=10)
+
+
+class CollectionSearchExtensionPostRequest(BaseModel):
+    """Collection Search extension POST request model."""
+
+    bbox: Optional[BBox]
+    datetime: Optional[DateTimeType]
+    limit: Optional[Limit] = Field(default=10)
diff --git a/stac_fastapi/extensions/tests/test_collection_search.py b/stac_fastapi/extensions/tests/test_collection_search.py
new file mode 100644
index 000000000..9703b4dc6
--- /dev/null
+++ b/stac_fastapi/extensions/tests/test_collection_search.py
@@ -0,0 +1,122 @@
+from typing import Iterator
+
+import pytest
+from stac_pydantic.api.collections import Collections
+from stac_pydantic.shared import BBox
+from starlette.testclient import TestClient
+
+from stac_fastapi.api.app import StacApi
+from stac_fastapi.extensions.core import CollectionSearchExtension
+from stac_fastapi.types.config import ApiSettings
+from stac_fastapi.types.core import BaseCollectionSearchClient, BaseCoreClient
+from stac_fastapi.types.rfc3339 import DateTimeType
+from stac_fastapi.types.search import (
+    BaseCollectionSearchGetRequest,
+    BaseCollectionSearchPostRequest,
+)
+from stac_fastapi.types.stac import Item, ItemCollection
+
+
+class DummyCoreClient(BaseCoreClient):
+    def all_collections(self, *args, **kwargs):
+        raise NotImplementedError
+
+    def get_collection(self, *args, **kwargs):
+        raise NotImplementedError
+
+    def get_item(self, *args, **kwargs):
+        raise NotImplementedError
+
+    def get_search(self, *args, **kwargs):
+        raise NotImplementedError
+
+    def post_search(self, *args, **kwargs):
+        raise NotImplementedError
+
+    def item_collection(self, *args, **kwargs):
+        raise NotImplementedError
+
+
+class DummyCollectionSearchClient(BaseCollectionSearchClient):
+    """Defines a pattern for implementing the STAC collection search extension."""
+
+    def get_collection_search(
+        self,
+        request: BaseCollectionSearchGetRequest,
+        bbox: BBox,
+        datetime: DateTimeType,
+        limit: int,
+    ):
+        return Collections()
+
+    def post_collection_search(
+        self, request: BaseCollectionSearchPostRequest, *args, **kwargs
+    ):
+        return Collections()
+
+
+def test_get_collection_search(client: TestClient) -> None:
+    get_search = client.get("/collection-search", params={"limit": 10})
+    assert get_search.status_code == 200, get_search.text
+    Collections(**get_search.json())
+
+
+def test_post_collection_search(client: TestClient) -> None:
+    post_search = client.post(
+        "/collection-search",
+        json={"limit": 10},
+    )
+    assert post_search.status_code == 200, post_search.text
+    Collections(**post_search.json())
+
+
+@pytest.fixture
+def client(
+    core_client: DummyCoreClient, collection_search_client: DummyCollectionSearchClient
+) -> Iterator[TestClient]:
+    settings = ApiSettings()
+    api = StacApi(
+        settings=settings,
+        client=core_client,
+        extensions=[
+            CollectionSearchExtension(client=collection_search_client, settings=settings),
+        ],
+    )
+    with TestClient(api.app) as client:
+        yield client
+
+
+@pytest.fixture
+def core_client() -> DummyCoreClient:
+    return DummyCoreClient()
+
+
+@pytest.fixture
+def collection_search_client() -> DummyCollectionSearchClient:
+    return DummyCollectionSearchClient()
+
+
+@pytest.fixture
+def item_collection(item: Item) -> ItemCollection:
+    return {
+        "type": "FeatureCollection",
+        "features": [item],
+        "links": [],
+        "context": None,
+    }
+
+
+@pytest.fixture
+def item() -> Item:
+    return {
+        "type": "Feature",
+        "stac_version": "1.0.0",
+        "stac_extensions": [],
+        "id": "test_item",
+        "geometry": {"type": "Point", "coordinates": [-105, 40]},
+        "bbox": [-105, 40, -105, 40],
+        "properties": {},
+        "links": [],
+        "assets": {},
+        "collection": "test_collection",
+    }
diff --git a/stac_fastapi/types/stac_fastapi/types/core.py b/stac_fastapi/types/stac_fastapi/types/core.py
index fdf020b08..21725bcb1 100644
--- a/stac_fastapi/types/stac_fastapi/types/core.py
+++ b/stac_fastapi/types/stac_fastapi/types/core.py
@@ -20,7 +20,10 @@
 from stac_fastapi.types.extension import ApiExtension
 from stac_fastapi.types.requests import get_base_url
 from stac_fastapi.types.rfc3339 import DateTimeType
-from stac_fastapi.types.search import BaseSearchPostRequest
+from stac_fastapi.types.search import (
+    BaseCollectionSearchPostRequest,
+    BaseSearchPostRequest,
+)
 
 NumType = Union[float, int]
 StacType = Dict[str, Any]
@@ -792,3 +795,79 @@ def get_queryables(
             "description": "Queryable names for the example STAC API Item Search filter.",
             "properties": {},
         }
+
+
+@attr.s
+class AsyncBaseCollectionSearchClient(abc.ABC):
+    """Defines a pattern for implementing the STAC Collection Search extension."""
+
+    @abc.abstractmethod
+    async def post_collection_search(
+        self, search_request: BaseCollectionSearchPostRequest, **kwargs
+    ) -> stac.ItemCollection:
+        """Cross catalog search (POST) of collections.
+
+        Called with `POST /collection-search`.
+
+        Args:
+            search_request: search request parameters.
+
+        Returns:
+            A tuple of (collections, next pagination token if any).
+        """
+        ...
+
+    @abc.abstractmethod
+    async def get_collection_search(
+        self,
+        bbox: Optional[BBox] = None,
+        datetime: Optional[DateTimeType] = None,
+        limit: Optional[int] = 10,
+        **kwargs,
+    ) -> stac.Collections:
+        """Cross catalog search (GET) of collections.
+
+        Called with `GET /collection-search`.
+
+        Returns:
+            A tuple of (collections, next pagination token if any).
+        """
+        ...
+
+
+@attr.s
+class BaseCollectionSearchClient(abc.ABC):
+    """Defines a pattern for implementing the STAC Collection Search extension."""
+
+    @abc.abstractmethod
+    def post_collection_search(
+        self, search_request: BaseCollectionSearchPostRequest, **kwargs
+    ) -> stac.Collections:
+        """Cross catalog search (POST) of collections.
+
+        Called with `POST /collection-search`.
+
+        Args:
+            search_request: search request parameters.
+
+        Returns:
+            A tuple of (collections, next pagination token if any).
+        """
+        ...
+
+    @abc.abstractmethod
+    def get_collection_search(
+        self,
+        bbox: Optional[BBox] = None,
+        datetime: Optional[DateTimeType] = None,
+        limit: Optional[int] = 10,
+        **kwargs,
+    ) -> stac.Collections:
+        """Cross catalog search (GET) of collections.
+
+        Called with `GET /collection-search`.
+
+        Returns:
+            A tuple of (collections, next pagination token if any).
+        """
+        ...
diff --git a/stac_fastapi/types/stac_fastapi/types/search.py b/stac_fastapi/types/stac_fastapi/types/search.py
index cf6647340..e001db35b 100644
--- a/stac_fastapi/types/stac_fastapi/types/search.py
+++ b/stac_fastapi/types/stac_fastapi/types/search.py
@@ -68,3 +68,18 @@ class BaseSearchPostRequest(Search):
     """Base arguments for POST Request."""
 
     limit: Optional[Limit] = 10
+
+
+@attr.s
+class BaseCollectionSearchGetRequest(APIRequest):
+    """Base arguments for Collection Search GET Request."""
+
+    bbox: Optional[BBox] = attr.ib(default=None, converter=str2bbox)
+    datetime: Optional[DateTimeType] = attr.ib(default=None, converter=str_to_interval)
+    limit: Optional[int] = attr.ib(default=10)
+    
+    
+class BaseCollectionSearchPostRequest(Search):
+    """Base arguments for Collection Search POST Request."""
+
+    limit: Optional[Limit] = 10