Jon Klassen (born November 29, 1981) is a Canadian writer and illustrator of children's books and an animator. He won both the American Caldecott Medal and the British Kate Greenaway Medal for children's book illustration, recognizing the 2012 picture book This Is Not My Hat, which he also wrote. He is the first person to win both awards for the same work.

This Is Not My Hat is a companion to Klassen's preceding picture book, I Want My Hat Back (2011), and his first as both writer and illustrator. Both books were on the New York Times Best Seller list for more than 40 weeks; by April 2014 one or the other had been translated into 22 languages and they had jointly surpassed one million worldwide sales. Both books were recommended for children ages 5+ by the Greenaway judges.