What is the purpose of the opening chorus in Romeo and Juliet?

This opening speech by the Chorus serves as an introduction to Romeo and Juliet. We are provided with information about where the play takes place, and given some background information about its principal characters.

The obvious function of the Prologue as introduction to the Verona of Romeo and Juliet can obscure its deeper, more important function. The Prologue does not merely set the scene of Romeo and Juliet, it tells the audience exactly what is going to happen in the play. The Prologue refers to an ill-fated couple with its use of the word "star-crossed," which means, literally, against the stars. Stars were thought to control people’s destinies. But the Prologue itself creates this sense of fate by providing the audience with the knowledge that Romeo and Juliet will die even before the play has begun. The audience therefore watches the play with the expectation that it must fulfill the terms set in the Prologue. The structure of the play itself is the fate from which Romeo and Juliet cannot escape.