English language science fiction young adult book series written by K. A. Applegate (Katherine Alice Applegate) and published by Scholastic. The first book of the series was published in 1996. Animorphs is the third-most successful children's book series of all time, after Harry Potter and Goosebumps. There was a single-book parody of Animorphs called Vegemorphs.
The series focuses on a group of human teenagers (along with an Andalite) who, with powers of shapeshifting ('morphing') granted upon them by alien technology, attempt to prevent the takeover of Earth by the Yeerks. To gain a new shapeshifting power, they must touch the chosen animal to absorb a length of the animal's DNA, enabling them to morph into that animal. The series is based primarily on Earth, though a few books have their primary setting in an alien environment.