Insidious: The Last Key is a 2018 American supernatural horror film directed by Adam Robitel and written by Leigh Whannell. It is produced by Jason Blum, Oren Peli, and James Wan. It is the fourth installment in the Insidious franchise, and the second in the chronology of the story running through the series. Starring Lin Shaye, Angus Sampson, Whannell, Spencer Locke, Caitlin Gerard, and Bruce Davison, the film follows parapsychologist Elise Rainier as she investigates a haunting in her childhood home. The film is the sequel to Insidious: Chapter 3 (2015) and the second prequel to Insidious (2010) and Insidious: Chapter 2 (2013).

Talks for a fourth installment in the franchise began in June 2015, with Whannell saying the next film would take place shortly before the first film. In May 2016, it was announced that Chapter 4 would have an October 2017 release date with Whannell writing, Blum, Peli and Wan producing, Robitel directing, and Shaye returning to reprise her role as Elise Rainier. Principal photography began in August 2016, and ended the following month.

The film was released in the United States on January 5, 2018, by Universal Pictures. It grossed $167 million worldwide and received mixed reviews. Insidious: The Red Door was released on July 7, 2023, continuing the storyline of the first two films.