A virelai is a form of medieval French verse used often in poetry and music. It is one of the three formes fixes (the others were the ballade and the rondeau), and was one of the most common verse forms set to music in Europe from the late 13th to the 15th centuries.

A virelai is similar to a rondeau. Each stanza has two rhymes, the end rhyme recurring as the first rhyme of the following stanza. The overall musical structure is almost invariably ABbaA, with the first and last sections having the same lyrics; this is the same form as the Italian ballata. The first stanza is known as the estribillo, the next two as mudanzas, and the fourth as the vuelta.

One of the most famous composers of virelai is Guillaume de Machaut (1300–1377), who also wrote his own verse; 33 separate compositions in the form survive by him. Other composers of virelai include Jehannot de l’Escurel, one of the earliest (d. 1304), and Guillaume Dufay (c.1400–1474), one of the last.

By the mid-15th century, the form had become largely divorced from music, and numerous examples of this form (as well as the ballade and the rondeau) were written, which were either not intended to be set to music, or for which the music has not survived.