Katherine Alice Applegate, known professionally as K. A. Applegate, is an American young adult and children's fiction writer, best known as the author of the Animorphs, Remnants, and Everworld book series. She won the 2013 Newbery Medal for her 2012 children's novel The One and Only Ivan.

Applegate's most popular books are in the genres of science fiction, fantasy, and adventure. She won the Best New Children's Book Series Award in 1997 from Publishers Weekly. Her book Home of the Brave has won several awards. She also wrote a chapter book series in 2008–09 called Roscoe Riley Rules.