The Butterfly Effect is a 2004 American science fiction thriller film written and directed by Eric Bress and J. Mackye Gruber. It stars Ashton Kutcher, Amy Smart, Eric Stoltz, William Lee Scott, Elden Henson, Logan Lerman, Ethan Suplee, and Melora Walters. The title refers to the butterfly effect.

Kutcher plays 20-year-old college student Evan Treborn, who experiences blackouts and memory loss throughout his childhood. Later, in his 20s, Evan finds he can travel back in time to inhabit his former self during those periods of blackout, with his adult mind inhabiting his younger body. He attempts to change the present by changing his past behaviors and set things right for himself and his friends, but there are unintended consequences for all. The film draws heavily on flashbacks of the characters' lives at ages 7 and 13 and presents several alternative present-day outcomes as Evan attempts to change the past, before settling on a final outcome.

The film had a poor critical reception; however, it was a commercial success, generating box-office revenues of $96 million on a budget of $13 million. The film won the Pegasus Audience Award at the Brussels International Fantastic Film Festival, and was nominated for Best Science Fiction Film at the Saturn Awards and Choice Movie: Thriller in the Teen Choice Awards, but lost to Eternal Sunshine of the Spotless Mind and The Texas Chainsaw Massacre, another film from New Line Cinema, respectively.