Sì is an operetta in three acts composed by Pietro Mascagni to a libretto by Carlo Lombardo with verses by Arturo Franci. The libretto is based on Lombardo's operetta La duchessa del Bal Tabarin and libretto for Majestät Mimi set by Bruno Granichstaedten in 1911. Mascagni's only venture into operetta, it premiered on 13 December 1919 at the Teatro Quirino in Rome. The operetta takes its name from its central character, Sì, an actress at the Folies Bergère, so called because she could never say no. ("Si" is the Italian word for "yes".)