Abby Ryder Fortson (born March 14, 2008) is an American child actress. She played Ella Novak in Transparent, Harper Weil in The Whispers, Sophie Pierson in Togetherness, Cassie Lang in Ant-Man (2015) and Ant-Man and the Wasp (2018), and Margaret Simon in Are You There God? It's Me, Margaret. (2023).

She is the daughter of actress Christie Lynn Smith and her husband, John Fortson.