diff --git a/causalpy/experiments/__init__.py b/causalpy/experiments/__init__.py
index 0548ada3..8318e6a5 100644
--- a/causalpy/experiments/__init__.py
+++ b/causalpy/experiments/__init__.py
@@ -11,3 +11,4 @@
 #   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 #   See the License for the specific language governing permissions and
 #   limitations under the License.
+"""Quasi-experimental designs for causal inference."""