The Makropulos Affair (also known as The Makropoulos Case, or The Makropulos Secret) is a three-act opera by Czech composer Leoš Janáček. The libretto, based on a play of the same name by Karel Čapek, was written by the composer between 1923 and 1925. The world premiere of the opera was given at the National Theatre in Brno on December 18, 1926, conducted by František Neumann.
The Makropulos Affair was his penultimate opera and, like much of his later work, it was inspired by his infatuation with Kamila Stösslová, a married woman much younger than himself. The lead character, Emillia Marty, is a 300 year old opera singer, daughter of an alchemist who created a formula for inmortality and tested it on his daughter. Emilia, however, is beginning to feel the effects of her age, and needs to get hold of the formula that will continue to elongate her life.