Iolanthe, or The Peer and the Peri, is a comic opera with music by Arthur Sullivan and libretto by W. S. Gilbert. It is one of the Savoy operas and the seventh collaboration of the fourteen between Gilbert and Sullivan. It was first produced in London at the Savoy Theatre, on 25 November 1882, three days after Patience closed, and ran for 398 performances.
At the time they wrote Iolanthe, both Gilbert and Sullivan were in their peak creative years, and Iolanthe, their seventh work together, drew the best from both composer and author. "[Sullivan] had composed a brilliant new score (his most subtle yet) to a scintillating libretto.... Iolanthe is the work in which Sullivan's operetta style takes a definite step forward, and metamorphosis of musical themes is its characteristic new feature.... By recurrence and metamorphosis of themes Sullivan made the score more fluid...."