"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.

A paucio/ribus autem quam a tribus uel saltem duobus non debet/ dici preter eos qui dicunt pedem.

Awe bleteþ after lomb lhouþ after calue cu Bulluc sterteþ bucke uerteþ murie sing cuccu

The ewe is bleating after her lamb, The cow is lowing after her calf; The bullock is prancing, The billy-goat farting, [or "The stag cavorting"[11]] Sing merrily, cuckoo!

The language used lacks all of the conventional springtime-renewal words of a reverdie (such as "green", "new", "begin", or "wax") except for springþ, and elements of the text, especially the cuckoo and the farmyard noises, potentially possess double meanings.

Platzer, on the other hand, views the latter, more vulgar, gloss as informed by "prejudices against mediæval culture" and suspects that those preferring it "may have had an axe to grind".

He knew that bullocks and bucks feel so good in the springtime that they can hardly contain themselves, and he set down what he saw and heard, leaving it to squeamish editors to distort one of his innocent folk-words into a meaning that he would not recognise.

[14] Similarly, Arthur K. Moore states: The older anthologists sometimes made ludicrous attempts to gloss 'buck uerteth' in a way tolerable to Victorian sensibilities.

The evolution of verteþ could not have originated in the unattested Old English feortan, in part because there is a gap of between 100 and 120 years between the first unambiguous usage of that word and its postulated use in Sumer is icumen in.

Given that the poem was likely composed in Reading, with Leominster as a second possibility, a quantitative analysis was performed using the Linguistic Atlas of Late Mediæval English; out of nine lexemes originally beginning with the letter F, six demonstrably retained that letter in Reading (the other three were unattested), while four retained it in Leominster (four unattested, with fetch evolving into vetch).

This also implies the existence of a word farten or ferten in Middle English, both with an initial letter F.[11] Beneath the Middle English lyrics in the manuscript,[6] there is also a set of Latin lyrics which consider the sacrifice of the Crucifixion of Jesus: Perspice Christicola† que dignacio Celicus agricola pro vitis vicio Filio non parcens exposuit mortis exicio Qui captivos semiuiuos a supplicio Vite donat et secum coronat in celi solio Observe, Christian, such honour!

[29] According to Lisa Colton, "Although it appears only this once, in that fleeting moment the tune serves to introduce the character through performance: the melody was presumably sufficiently recognisable to be representative of medieval English music, but perhaps, more importantly, the fact that Little John is whistling the song emphasizes his peasant status...In Robin Hood, Little John's performance of 'Sumer is icumen in' locates him socially as a contented, lower class male, a symbol of the romanticized ideal of the medieval peasant".

[30] The rendition sung at the climax of the 1973 British film The Wicker Man[31] is a mixed translation by Anthony Shaffer:[32] Sumer is Icumen in, Loudly sing, cuckoo!

Ewe bleats harshly after lamb, Cows after calves make moo; Bullock stamps and deer champs, Now shrilly sing, cuckoo!

[34] In The Loathsome Lambton Worm, the unproduced script treatment for a sequel of The Wicker Man, Pound's variant of the poem was used in the place of the original.

[35] Winter is icumen in, Lhude sing Goddamm, Raineth drop and staineth slop, And how the wind doth ramm!

The song is also parodied by "P. D. Q. Bach" (Peter Schickele) as "Summer is a cumin seed" for the penultimate movement of his Grand Oratorio The Seasonings.