Horton Hears a Who! is a 2008 American animated adventure comedy film based on the 1954 book of the same name by Dr. Seuss, produced by Blue Sky Studios and distributed by 20th Century Fox. The film was directed by Jimmy Hayward and Steve Martino, from a screenplay written by the writing team of Cinco Paul and Ken Daurio. It stars the voices of Jim Carrey and Steve Carell as Horton the Elephant and Mayor Ned McDodd, respectively, alongside Carol Burnett, Will Arnett, Seth Rogen, Dan Fogler, Isla Fisher, Jonah Hill, and Amy Poehler. Recurring Blue Sky collaborator John Powell composed the film's musical score. It is the fourth screen adaptation of the book following the 1970 Chuck Jones television special, the 1987 Soviet animated short, and the 1992 Russian animated short.

Horton Hears a Who! is a children's book written and illustrated by Theodor Seuss Geisel under the pen name Dr. Seuss. It was published in 1954 by Random House. This book tells the story of Horton the Elephant and his adventures saving Whoville, a tiny planet located on a speck of dust, from the animals who mock him. These animals attempt to steal and burn the speck of dust, so Horton goes to great lengths to save Whoville from being incinerated.