The Blair Witch Project is a 1999 American psychological horror film written, directed, and edited by Daniel Myrick and Eduardo Sánchez. One of the most successful independent films of all time, it is a "found footage" mockumentary in which three students (Heather Donahue, Michael C. Williams, and Joshua Leonard) hike into the Black Hills near Burkittsville, Maryland, to shoot a documentary about a local myth known as the Blair Witch.

Myrick and Sánchez conceived of a fictional legend of the Blair Witch in 1993. They developed a 35-page screenplay with the dialogue to be improvised. A casting call advertisement on Backstage magazine was prepared by the directors; Donahue, Williams, and Leonard were cast. The film entered production in October 1997, with the principal photography lasting eight days. Most of the filming was done on the Greenway Trail along Seneca Creek in Montgomery County, Maryland. About 20 hours of footage was shot, which was edited down to 82 minutes. Shot on an original budget of $35,000–60,000, the film had a final cost of $200,000–750,000 after post-production and marketing.

When The Blair Witch Project premiered at the Sundance Film Festival at midnight on January 23, 1999, its promotional marketing campaign listed the actors as either "missing" or "deceased". Due to its successful Sundance run, Artisan Entertainment bought the film's distribution rights for $1.1 million. The film had a limited release on July 14 of the same year, before expanding to a wider release starting on July 30. While the film received critical acclaim, audience reception was polarized.

The Blair Witch Project was a sleeper hit. It grossed nearly $250 million worldwide and is consistently listed as one of the scariest movies of all time. Despite the success, the three main actors had reportedly lived in poverty. In 2000, they sued Artisan Entertainment claiming unfair compensation, eventually reaching a $300,000 settlement. The Blair Witch Project launched a media franchise, which includes two sequels (Book of Shadows and Blair Witch), novels, comic books, and video games. It revived the found-footage technique and influenced similarly successful horror films such as Paranormal Activity (2007), REC (2007) and Cloverfield (2008).