Saw is a 2004 American horror film directed by James Wan, in his feature directorial debut, and written by Leigh Whannell from a story by Wan and Whannell. It is the first installment in the Saw film series, and stars Whannell alongside Cary Elwes, Danny Glover, Monica Potter, Michael Emerson, and Ken Leung.

The film tells a nonlinear narrative revolving around the mystery of the Jigsaw Killer, who tests his victims' will to live by putting them through deadly "games" where they must inflict great physical pain upon themselves to survive. The frame story follows Jigsaw's latest victims (Whannell and Elwes), who awaken in a large, dilapidated bathroom, with one being ordered to kill the other to save his own family.

The screenplay was written by Whannell, who co-created the story with Wan in their respective screenwriting debuts. The film was originally written in 2001, but after failed attempts to get the script produced in Wan and Whannell's home country of Australia, they were urged to travel to Los Angeles. In order to help attract producers, they shot a low-budget short film of the same name from a scene out of the script. This proved successful in 2003 as producers from Evolution Entertainment were immediately attached and also formed a horror genre production label, Twisted Pictures. The film was given a small production budget and was shot in 18 days.

Saw was first screened on January 19, 2004, at the 2004 Sundance Film Festival. Due to positive audience reception, Lionsgate picked up the distribution rights for the film. Originally planned for a straight-to-video release, they decided to instead release the film in theaters in North America on October 29, 2004. The film received generally mixed reviews from critics. After topping the opening weekend box office, the film would go on to gross $103.9 million worldwide to become one of the most profitable horror films since Scream (1996). A sequel, titled Saw II, released the following year, and a direct sequel, titled Saw X, released in 2023.

It was theatrically re-released to select theaters, on October 31, 2014, for its tenth anniversary. The success of Saw launched a media franchise, including several films, video games, theme park rides, and merchandising.