Public Domain in most countries other than the UK.
'Sumer Is Icumen In', a musical composition for several voices, was probably composed at Reading Abbey around the middle of the 13th century. This song, written in Middle English, was meant to be sung in the round, with four voices singing the same melody one after the other, accompanied by two lower voices.
The song is the oldest known musical round with English words. It survives in only a single manuscript probably made in Oxford during the 3rd quarter of the 13th century. The way the song is set allows singers to choose between the Middle English lyrics, celebrating the arrival of spring, and the lyrics in Latin, which are religious. This is the earliest surviving example of a piece of music in which both secular and sacred words are written to the same piece of music. The text to the right of the page gives instructions in Latin for its performance as a round, the cross above the first line marking the point at which each of the four main voices enters.
The Middle English text includes many familiar animal names such as cuccu (cuckoo), lomb (lamb) and cu (cow). Famously the bucke (buck) is said to farteth: the first record of the verb 'to fart'.