La clemenza di Tito (The Clemency of Titus), K. 621, is an opera seria in two acts composed by Wolfgang Amadeus Mozart to an Italian libretto by Caterino Mazzolà, after Pietro Metastasio. It was started after most of Die Zauberflöte (The Magic Flute), the last of Mozart's principal operas, had already been written. The work premiered on 6 September 1791 at the Estates Theatre in Prague.