What is the purpose of an overture in an opera performance?

An overture is an orchestral introduction to an opera, serving several evolving purposes throughout musical history. While early examples functioned primarily to signal the start of a performance and capture the audience's attention, the role of the overture expanded significantly over time.1

By the 18th century, composers like Christoph Gluck established that the overture should prepare the audience for the drama to follow by setting the appropriate emotional tone. This approach often involved thematic anticipation, where composers such as Wolfgang Amadeus Mozart and Ludwig van Beethoven incorporated musical themes from the opera into the overture itself.1

In some works, the overture serves as a seamless transition, merging directly into the music and mood of the opening act rather than concluding before the curtain rises. By the late 19th century, the traditional overture was frequently replaced by a shorter, free-form prelude designed to lead directly into the opening scene.1