Blue Murder at St Trinian's is a 1957 British comedy film, directed by Frank Launder, co-written by Launder and Sidney Gilliat, and starring Terry-Thomas, George Cole, Joyce Grenfell, Lionel Jeffries and Richard Wattis; the film also includes a brief cameo of Alastair Sim, reprising his lead role in the 1954 film, The Belles of St. Trinian's. Inspired by the St Trinian's School comic strips by British cartoonist Ronald Searle, the film is the second entry in the St. Trinian's film series, with its plot seeing the students of the fictional school making plans to secure a place on a European tour, all while subsequently aiding a criminal who is secretly seeking to escape the country with stolen jewels.

The film received generally positive reviews from critics, with praise given to the evolution of the comedy following the first film. It was later succeeded by a sequel, The Pure Hell of St Trinian's, in 1960.