Zak Penn (born March 23, 1968) is an American screenwriter. Penn wrote and directed Incident at Loch Ness and The Grand, wrote the script for The Incredible Hulk, co-wrote the scripts for X2 and X-Men: The Last Stand, and the story for The Avengers.

With Michael Karnow, Penn is the co-creator of the TV series Alphas on the Syfy network. Penn was born in New York. He is the son of New York businessman and lawyer Arthur Penn, who led the acquisition of the Capital Markets Assurance Corporation from Citicorp.