Sumer is icumen in

"Sumer is icumen in" is the incipit of a medieval English round or rota of the mid-13th century; it is also known variously as the Summer Canon and the Cuckoo Song.

The line translates approximately to "Summer has come" or "Summer has arrived". The song is written in the Wessex dialect of Middle English. Although the composer's identity is unknown today, it may have been W. de Wycombe or a monk at Reading Abbey, John of Fornsete. The manuscript in which it is preserved was copied between 1261 and 1264.

This rota is the oldest known musical composition featuring six-part polyphony.

It is sometimes called the Reading Rota because the earliest known copy of the composition, a manuscript written in mensural notation, was found at Reading Abbey; it was probably not drafted there, however. The British Library now retains this manuscript. A copy of the manuscript in stone relief is displayed on the wall of the ruined chapter house of Reading Abbey.