I'll Be Your Sweetheart is a 1945 British historical musical film directed by Val Guest and starring Margaret Lockwood, Vic Oliver and Michael Rennie. It was the first and only musical film produced by Gainsborough Studios. Commissioned by the British Ministry of Information, it was set at the beginning of the 20th century, and was about the composers of popular music hall songs fighting for a new copyright law that will protect them from having their songs stolen. Copyright scholar Adrian Johns has called the film "propaganda" and "a one-dimensional account of the piracy crisis [about sheet music in the early 20th century] from the publishers' perspective", but also highlighted its value as historical document, with large parts of the dialogue "closely culled from the actual raids, court cases, and arguments of 1900-1905."