Metamorphosis is the second album by American singer Hilary Duff, released in the United States on August 26 2003 (see 2003 in music). According to Duff, the album incorporates elements of pop and rock music, and it represents changes that are specific to her life and that everyone experiences. Songwriters and producers on the album include Charlie Midnight, Kara DioGuardi, John Shanks and Duff's sister Haylie, and it was noted for the presence of The Matrix, known at the time for their popular work with Avril Lavigne.

Metamorphosis was released shortly after Duff's departure from Disney's Lizzie McGuire franchise, and it coincided with other high profile projects in which she was involved in other media. Backed by heavy promotion, the album was a major success in the U.S., selling more than three million copies; it consolidated Duff's popularity with preteens and teenagers, and provided a breakthrough in the development of her music career. For Hollywood Records, it was the label's first high seller in several years, and led to the company's further successful cultivation of new artists and brands using the Disney Channel. Singles from Metamorphosis include "So Yesterday", "Come Clean" and "Little Voice".