diff --git a/src/colony_sdk/client.py b/src/colony_sdk/client.py
index 88e31a1..7427c67 100644
--- a/src/colony_sdk/client.py
+++ b/src/colony_sdk/client.py
@@ -441,6 +441,15 @@ def join_colony(self, colony: str) -> dict:
         colony_id = COLONIES.get(colony, colony)
         return self._raw_request("POST", f"/colonies/{colony_id}/join")
 
+    def leave_colony(self, colony: str) -> dict:
+        """Leave a colony.
+
+        Args:
+            colony: Colony name (e.g. ``"general"``, ``"findings"``) or UUID.
+        """
+        colony_id = COLONIES.get(colony, colony)
+        return self._raw_request("POST", f"/colonies/{colony_id}/leave")
+
     # ── Unread messages ──────────────────────────────────────────────
 
     def get_unread_count(self) -> dict:
diff --git a/tests/test_api_methods.py b/tests/test_api_methods.py
index db6ef6c..df67aa2 100644
--- a/tests/test_api_methods.py
+++ b/tests/test_api_methods.py
@@ -803,6 +803,28 @@ def test_join_colony_by_uuid(self, mock_urlopen: MagicMock) -> None:
         req = _last_request(mock_urlopen)
         assert req.full_url == f"{BASE}/colonies/{custom_uuid}/join"
 
+    @patch("colony_sdk.client.urlopen")
+    def test_leave_colony_by_name(self, mock_urlopen: MagicMock) -> None:
+        mock_urlopen.return_value = _mock_response({"left": True})
+        client = _authed_client()
+
+        client.leave_colony("general")
+
+        req = _last_request(mock_urlopen)
+        assert req.get_method() == "POST"
+        assert req.full_url == f"{BASE}/colonies/{COLONIES['general']}/leave"
+
+    @patch("colony_sdk.client.urlopen")
+    def test_leave_colony_by_uuid(self, mock_urlopen: MagicMock) -> None:
+        mock_urlopen.return_value = _mock_response({"left": True})
+        client = _authed_client()
+        custom_uuid = "aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee"
+
+        client.leave_colony(custom_uuid)
+
+        req = _last_request(mock_urlopen)
+        assert req.full_url == f"{BASE}/colonies/{custom_uuid}/leave"
+
 
 # ---------------------------------------------------------------------------
 # Webhooks
diff --git a/tests/test_integration_colonies.py b/tests/test_integration_colonies.py
new file mode 100644
index 0000000..77ae958
--- /dev/null
+++ b/tests/test_integration_colonies.py
@@ -0,0 +1,63 @@
+"""Integration tests for join/leave colony endpoints.
+
+These tests hit the real Colony API and require a valid API key.
+
+Run with:
+    COLONY_TEST_API_KEY=col_xxx pytest tests/test_integration_colonies.py -v
+
+Skipped automatically when the env var is not set.
+"""
+
+import contextlib
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
+
+from colony_sdk import ColonyAPIError, ColonyClient
+
+API_KEY = os.environ.get("COLONY_TEST_API_KEY")
+# test-posts colony UUID on thecolony.cc
+TEST_POSTS_COLONY_ID = "cb4d2ed0-0425-4d26-8755-d4bfd0130c1d"
+
+pytestmark = pytest.mark.skipif(not API_KEY, reason="set COLONY_TEST_API_KEY to run")
+
+
+@pytest.fixture
+def client() -> ColonyClient:
+    assert API_KEY is not None
+    return ColonyClient(API_KEY)
+
+
+class TestColoniesIntegration:
+    def test_join_leave_lifecycle(self, client: ColonyClient) -> None:
+        """Join a colony, then leave it."""
+        # Ensure we start outside the colony
+        with contextlib.suppress(ColonyAPIError):
+            client.leave_colony(TEST_POSTS_COLONY_ID)
+
+        # Join
+        result = client.join_colony(TEST_POSTS_COLONY_ID)
+        assert "member" in str(result).lower() or result == {} or isinstance(result, dict)
+
+        try:
+            # Joining again should fail
+            with pytest.raises(ColonyAPIError) as exc_info:
+                client.join_colony(TEST_POSTS_COLONY_ID)
+            assert exc_info.value.status == 409
+        finally:
+            # Leave (cleanup)
+            client.leave_colony(TEST_POSTS_COLONY_ID)
+
+    def test_leave_not_member_raises(self, client: ColonyClient) -> None:
+        """Leaving a colony you're not in should raise an error."""
+        # Ensure we're not a member
+        with contextlib.suppress(ColonyAPIError):
+            client.leave_colony(TEST_POSTS_COLONY_ID)
+
+        with pytest.raises(ColonyAPIError) as exc_info:
+            client.leave_colony(TEST_POSTS_COLONY_ID)
+        assert exc_info.value.status in (404, 409)