Demon Slayer: Kimetsu no Yaiba – The Movie: Mugen Train (Japanese: 劇場版 鬼滅の刃 無限列車編, Hepburn: Gekijō-ban Kimetsu no Yaiba Mugen Ressha-hen), also known simply as Demon Slayer: Mugen Train, is a 2020 Japanese animated dark fantasy action film based on the "Mugen Train" arc of the 2016–20 manga series Demon Slayer: Kimetsu no Yaiba by Koyoharu Gotouge. It is a direct sequel to the first season of the anime television series as well as its first film adaptation. The film was directed by Haruo Sotozaki and written by Ufotable staff members.

Demon Slayer: Kimetsu no Yaiba – The Movie: Mugen Train was released during the COVID-19 pandemic, premiering in Japan on October 16, 2020, by Toho and Aniplex, and late 2020 to mid-2021 internationally. The film was a critical and commercial success, grossing over $507 million worldwide and making it the highest-grossing film of 2020. It marked the first time ever that a non-American production topped the annual global box office, and it set a number of box office records, including becoming the highest-grossing Japanese film of all time, a title previously held by Spirited Away (2001). It also has received numerous awards, including Animation of the Year at the 44th Japan Academy Film Prize as well as the Best Animation Film at the 45th Hochi Film Award.

A sequel set after the events of the second season, Demon Slayer: Kimetsu no Yaiba – To the Swordsmith Village, was released on February 3, 2023, with a third film set after the events of the third season, Demon Slayer: Kimetsu no Yaiba – To the Hashira Training, released on February 2, 2024. A film trilogy set after the events of the fourth season, Demon Slayer: Kimetsu no Yaiba – The Movie: Infinity Castle, is in development.