Aucassin et Nicolette, ou Les moeurs du bon vieux tems is a French comédie mise en musique in four acts by André Grétry. The work was first performed by the Comédie-Italienne at the Palace of Versailles on 30 December 1779 and at the Hôtel de Bourgogne in Paris on 3 January 1780.
The libretto was by Michel-Jean Sedaine after the early medievalist Jean-Baptiste de La Curne de Sainte-Palaye's Les amours du bon vieux tems.