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.

"A person's a person, no matter how small" is the most popular line from Horton Hears a Who! and also serves as the major moral theme that Dr. Seuss conveys to his audience. Horton endures harassment to care for and ensure the safety of the Whos, who represent the insignificant. Horton Hears a Who! has been well-received in libraries, schools, and homes across the world. The book has been adapted as a 1970 television special and a 2008 animated film by Blue Sky Studios and Twentieth Century Fox Animation, and much of its plot was incorporated into the Broadway musical production Seussical.