Mac Barnett and Jon Klassen have made five books together: Sam and Dave Dig a Hole, Extra Yarn, The Wolf, the Duck and the Mouse, Triangle and this book, Square.

Jon is also the creator of the much-acclaimed Hat trilogy, which includes I Want My Hat Back, the Kate Greenaway and Caldecott Medal winner This Is Not My Hat and We Found a Hat.

They both live in California, USA, but in different cities. Jon is from Canada, Mac is not.

Greg Pizzoli is an author, illustrator, and printmaker. His first picture book, The Watermelon Seed, won the Theodor Seuss Geisel Award, and his book Good Night Owl was a Geisel Honor. His Viking nonfiction picture book Tricky Vic was a New York Times Best Illustrated of 2015. He lives in Philadelphia.