Old is a 2021 American horror mystery film written, directed, and produced by M. Night Shyamalan. It is based on the French-language Swiss graphic novel Sandcastle by Pierre Oscar Lévy and Frederik Peeters. The film features an ensemble cast consisting of Gael García Bernal, Vicky Krieps, Rufus Sewell, Alex Wolff, Thomasin McKenzie, Abbey Lee, Nikki Amuka-Bird, Ken Leung, Eliza Scanlen, Aaron Pierre, Embeth Davidtz, and Emun Elliott. The plot follows a group of people who find themselves aging rapidly on a secluded beach.

Shyamalan decided to adapt Sandcastle into a film after receiving it as a Father's Day gift in 2017. The untitled project was announced in September 2019, with the filmmaker revealing a partnership with Universal Pictures. The following year, filming took place in the Dominican Republic for three months, during the COVID-19 pandemic, with cinematographer Michael Gioulakis.

Old premiered at Jazz at Lincoln Center in New York City on July 19, 2021, and was theatrically released in the United States on July 23. The film grossed $90 million worldwide against an $18 million budget and received mixed reviews from critics.