Mo Willems is an American writer, animator, voice actor, and children's book author. He is best known for his Caldecott Honor-winning picture books, Don't Let the Pigeon Drive the Bus! and Knuffle Bunny: A Cautionary Tale.

Willems was born in the Chicago suburb of Des Plaines, Illinois, and was raised in New Orleans. He graduated cum laude from New York University's Tisch School of the Arts. His work includes creating the animated television series Sheep in the Big City for Cartoon Network, working on Sesame Street and The Off-Beats, and creating the children's book series Elephant and Piggie.

Three of Willems' books have been awarded a Caldecott Honor: Don't Let the Pigeon Drive the Bus!, Knuffle Bunny: A Cautionary Tale, and Knuffle Bunny Too: A Case of Mistaken Identity. The third book also won the Indies Choice Book Award for Children's Illustrated Book.

In addition to his picture books, Mo Willems has created the Elephant and Piggie books, a series of early readers, and published You Can Never Find a Rickshaw When it Monsoons, an annotated cartoon journal sketched during a year-long voyage around the world in 1990-91.

His works have been translated into numerous languages and have inspired animated shorts. The New York Times Book Review called Mo "the biggest new talent to emerge thus far in the 00's."