diff --git a/api/api.go b/api/api.go
index c2c9689..6813b5a 100644
--- a/api/api.go
+++ b/api/api.go
@@ -49,6 +49,8 @@ func NewCustomClient(token string, httpClient *httputil.Client) *Client {
 	}
 }
 
+// WithContext returns a shallow copy of Client with the given context. It's
+// used for method timeouts and such. This method is thread-safe.
 func (c *Client) WithContext(ctx context.Context) *Client {
 	return &Client{
 		Client:  c.Client.WithContext(ctx),
diff --git a/state/state.go b/state/state.go
index 6505422..47341a2 100644
--- a/state/state.go
+++ b/state/state.go
@@ -76,6 +76,9 @@ func NewFromSession(s *session.Session, store Store) (*State, error) {
 	return state, state.hookSession()
 }
 
+// WithContext returns a shallow copy of State with the context replaced in the
+// API client. All methods called on the State will use this given context. This
+// method is thread-safe.
 func (s *State) WithContext(ctx context.Context) *State {
 	copied := *s
 	copied.Client = copied.Client.WithContext(ctx)