Thomas & Friends: Sodor's Legend of the Lost Treasure is a 2015 British animated fantasy adventure comedy film and the ninth feature-length special movie of the British television series, Thomas & Friends. The film is produced by HIT Entertainment and animated by Arc Productions.

The film stars the voices of Joseph May and John Hasler as the voice of Thomas in the US and UK dubs respectively. It stars the voices of Olivia Colman, Keith Wickham, Tim Whitnall, Rob Rackstraw, William Hope, Kerry Shale, Christopher Ragland, Glenn Wrage, Joe Mills, Teresa Gallagher, Jules de Jongh, Steven Kynman and Tom Stourton in supporting roles.

Eddie Redmayne, Sir John Hurt, Jamie Campbell Bower and Nathan Clarke join the series’ voice cast, although only Bower and Clarke would continue to be involved in future projects. The film marks the screen debuts of Rex, Bert and Mike, the Arlesdale Railway engines, the central characters of the Reverend Wilbert Awdry's book, Small Railway Engines. The three characters, based on real locomotives from the Ravenglass and Eskdale Railway, had previously only appeared in The Railway Series and had been omitted from the TV show. Several characters who had been absent from the television series for many years also make their return.

The film also features a cameo appearance from a fictionalized version of Wilbert Awdry, the author of the original books. The film received a theatrical release in the UK during July 2015 and in Australia during August, and was released on DVD on September 19. It was met with mostly positive reviews from critics, who praised the direction and solid plot but one critical of the film's somewhat dark undertone.