Thomas & Friends: Sodor's Legend of the Lost Treasure is a 2015 British animated fantasy adventure film and the ninth feature-length special in the Thomas & Friends television series. The film is produced by HIT Entertainment with animation production by Arc Productions. The film centres on Thomas unwillingly getting caught in a conspiracy to steal recently-discovered pirate treasure.

The film stars John Hasler (UK) and Joseph May (US) as the voice of Thomas, alongside special guest stars Sir John Hurt as the film's main antagonist Sailor John and Eddie Redmayne as the purple tank engine Ryan. It also stars Jamie Campbell Bower as Skiff the sailboat, who would later reprise his role in the series. The film also marks the screen debut of Rex, Mike and Bert, who appeared in the twenty-second book of The Railway Series, "Small Railway Engines", and are based on locomotives from the Ravenglass and Eskdale Railway. Several other characters who had made long absences in the TV series, such as Donald, Douglas, Daisy and select members of the Sodor Construction Company, make their return in the film.

The film received a limited theatrical release in the United Kingdom in July 2015. It was met with mostly positive reviews from critics, who praised the direction and plot but were critical of the film's somewhat dark undertone.