The Palais Garnier, also known as Opéra Garnier, is a historic 1,979-seat opera house at the Place de l'Opéra in the 9th arrondissement of Paris, France. It was built for the Paris Opera from 1861 to 1875 at the behest of Emperor Napoleon III. Initially referred to as le nouvel Opéra de Paris, it soon became known as the Palais Garnier, "in acknowledgment of its extraordinary opulence" and the architect Charles Garnier's plans and designs, which are representative of the Napoleon III style. It was the primary theatre of the Paris Opera and its associated Paris Opera Ballet until 1989, when a new opera house, the Opéra Bastille, opened at the Place de la Bastille. The company now uses the Palais Garnier mainly for ballet. The theatre has been a monument historique of France since 1923.

An opera house is a theater building used for performances of opera. Like many theaters, it usually includes a stage, an orchestra pit, audience seating, backstage facilities for costumes and building sets, as well as offices for the institution's administration.