This Is Not My Hat is a 2012 American children's picture book by the author and illustrator Jon Klassen.

It is a thematic follow-up to I Want My Hat Back (2011) and was meant to be a more literal sequel until Klassen took a suggestion to change which animals were in the story.

The book was well received by critics, who praised its dark or ironic humor which could only be understood by comparing the words of the little fish's narration against the events of the illustrations.

[1] Klassen also felt that this story was more "dramatic" than his earlier work and cited "The Tell-Tale Heart" as a thematic inspiration.

[2][3] For this book he sketched the illustrations in ink before digitizing them and finishing the colors and details electronically.

[9][10] The small fish, acting as the book's narrator through its monologue, is not only amoral but also "outrageous" in the claims that it will not get caught.

[17] In a "highly recommend" review for Library Media Connection librarian Lisa Wright writes, "The narrative parallels the illustrations as the reader deduces the facts of the actual theft.

[8] The book spent more than forty weeks on The New York Times Best Seller list and the combined sales of it and I Want My Hat Back were more than 1.5 million copies.