Thirteen is a 2003 teen drama film directed by Catherine Hardwicke, written by Hardwicke and Nikki Reed, and starring Holly Hunter, Evan Rachel Wood and Reed with Jeremy Sisto, Brady Corbet, Deborah Kara Unger, Kip Pardue, Sarah Clarke, D. W. Moffett, Vanessa Hudgens (in her film acting debut), and Jenicka Carey in supporting roles. Loosely based on Reed's life from ages 12 to 13, the film's plot follows Tracy, a seventh-grade student in Los Angeles who begins dabbling in substance abuse, sex, self-harm, and crime after being befriended by a troubled classmate.

The screenplay for Thirteen was written over six days by Hardwicke and the then-14-year-old Reed; Hardwicke, a former production designer, marking her directorial debut, independently raised funds herself for the production.

Upon the film's debut at the Sundance Film Festival in January 2003, Hardwicke won the Sundance Directing (Drama) for the film. Fox Searchlight Pictures subsequently acquired Thirteen for distribution, giving the film a limited release in the United States beginning on August 20, 2003; the release would expand in September 2003 and the film went on to gross a total of $4.6 million at the U.S. box office.

Though it received numerous favorable reviews from critics, Thirteen generated some controversy for its depiction of youth drug use (including inhalants, marijuana, LSD and alcohol), underage sexual behavior, and self-harm. The film earned Hunter an Academy Award nomination for Best Supporting Actress and Golden Globe nominations for Hunter and Wood for Best Supporting Actress and Best Actress in a Drama, respectively.