James Muir Mathieson, OBE (24 January 1911 – 2 August 1975) was a British musician whose career was spent mainly as the musical director for British film studios.

Born in Scotland, to a musical family, Mathieson won a scholarship to the Royal College of Music in London. His teachers there included Malcolm Sargent, who recommended him to the film producer Alexander Korda, whose musical director he became in 1934. Mathieson made most of his career in the film industry. After the Second World War he was musical director to the Rank Organisation.

Among the composers from whom Mathieson commissioned film scores were Arthur Bliss, Ralph Vaughan Williams, William Walton and Benjamin Britten. Mathieson rarely wrote the music for the films on which he worked, considering himself to lack the talent for original composition, but he helped the composers who wrote for him to make their material precisely fit the action of the film, and he arranged concert suites from some of the scores he commissioned. He was responsible as musical director, arranger, conductor or occasionally composer for nearly a thousand films.