Mo Willems (born February 11, 1968) is an American writer, animator, voice actor, and creator of children's books. His television work includes creating the animated television series Sheep in the Big City for Cartoon Network as well as working on Sesame Street, and The Off-Beats.

Since 2003, Willems has authored numerous books for young children, many of which have garnered significant critical acclaim. The New York Times Book Review referred to Willems as "the biggest new talent to emerge thus far in the 00's" — and to his pigeon character as "one of this decade's contributions to the pantheon of great picture book characters." He also creates the Elephant and Piggie books, an early reader series about a friendly elephant and pig. In 2010, Willems introduced a new series of books featuring Cat the Cat, also aimed at early readers.