Primer is a 2004 American independent science fiction film about the accidental discovery of time travel. The film was written, directed, produced, edited and scored by Shane Carruth in his debut feature. Carruth also stars with David Sullivan.

Primer is noted for its extremely low budget, experimental plot structure, philosophical implications, and complex technical dialogue, which Carruth, a college graduate with a degree in mathematics and a former engineer, chose not to simplify for the sake of the audience. The film collected the Grand Jury Prize Dramatic at the 2004 Sundance Film Festival, before securing a limited release in the United States, and has since gained a cult following.