Triangle is a 2009 psychological horror film written and directed by Christopher Smith and starring Melissa George, Michael Dorman, Rachael Carpani, Henry Nixon, Emma Lung, and Liam Hemsworth. George portrays a single mother who goes on a boating trip with several friends. When they are forced to abandon their ship, they board a derelict ocean liner, where they become convinced that someone is stalking them.

A British-Australian co-production, the film was financed by UK Film Council that awarded £1.6 million ($2.8 million) of public money from the National Lottery fund towards the development, production and distribution of the film. The film was based in part on the story of Sisyphus, the Greek mythological figure cursed to repeatedly push a boulder up a hill without ever successfully reaching the top. Smith also was inspired by Dead of Night (1945) and Memento (2000). He wanted to make a circular film that explored déjà vu, while avoiding reusing elements of Jacob's Ladder (1990). The film was shot on sets and on location in Queensland, Australia. Smith insisted on having a set constructed that depicted the exterior of a cruise liner, in order to minimize shooting in front of green screens.

Triangle premiered at the London FrightFest Film Festival on 27 August 2009, and was released theatrically in the UK on 16 October 2009. The film received generally positive reviews from film critics and grossed $1.3–1.6 million worldwide.