Thésée (French: [tese]; lit. 'Theseus') is a tragédie en musique, an early type of French opera, in a prologue and five acts with music by Jean-Baptiste Lully and a libretto by Philippe Quinault based on Ovid's Metamorphoses. It was first performed on 11 January 1675 by the Paris Opera for the royal court at the Château de Saint-Germain-en-Laye and was first performed in public in April at the Théâtre du Palais-Royal in Paris.

The plot centres around a love triangle: Aegeus wants to marry his ward, princess Aegle, while the sorceress Medea wishes to marry the young warrior Theseus, but Theseus and Aegle love each other. Medea attempts to force the lovers to renounce each other: first by using her magic to bring Aegle to a place of torment, then by convincing Aegeus to have Theseus killed as a potential threat to his reign. But before Theseus can drink the poison he has been given, Aegeus realises that Theseus is his lost son. He then gives Aegle to Theseus. Medea takes vengeance by destroying the festive setting, but the goddess Minerva undoes this.