"This Is Not My Hat" is a children's picture book written and illustrated by Jon Klassen. The story follows a small fish who steals a hat from a larger fish while claiming that it is not his. The narrative is simple yet engaging, with a focus on themes of deception and consequences. The illustrations in the book are minimalistic, using a limited color palette to enhance the storytelling. As the small fish swims away, readers can see hints of what might happen next, creating a sense of suspense. The book has received critical acclaim and won the Caldecott Medal for its artistic merit.