The Mousetrap is a murder mystery play by Agatha Christie. The Mousetrap opened in London's West End in 1952 and ran continuously until 16 March 2020, when the stage performances had to be temporarily discontinued during the COVID-19 pandemic. It then re-opened on 17 May 2021. The longest-running West End show, it has by far the longest run of any play in the world, with its 28,915th performance having taken place as of November 2022. Attendees at St Martin's Theatre often get their photo taken beside the wooden counter (showing a count of the number of performances) in the theatre foyer. As of 2022 the play has been seen by 10 million people in London.

A "Whodunit", the play has a twist ending, which the audience are traditionally asked not to reveal after leaving the theatre. There are eight members of the cast, and by 2012 more than 400 actors and actresses had played the roles. Richard Attenborough was the original Detective Sergeant Trotter, and his wife, Sheila Sim, the first Mollie Ralston – owner of Monkswell Manor guesthouse. However since then few of the cast have been headliners, with Stephen Moss in The Guardian writing, "the play and its author are the stars".