Gaudete was made (relatively) famous in the 1970s when it was performed and recorded by the folk rock group "Steeleye Span", and ever since it has been included in a large number of Christmas collections (it is, after all, a Christmas song, although many AICSAns may not realise this).
The original author is of "Gaudete" is unknown, although it is sometimes mistakenly attributed to a composer by the name of "Piae Cantiones". Piae Cantiones was in fact a songbook published in Finland in 1582, which contained the first published edition of Gaudete. The songbook had the full title of "Piae Cantiones Ecclesiasticae et Scholasticae Veterum Episcoporum" (Devout ecclesiastical and scholastic songs of the old bishops), and contained a collection of Latin songs, intended for the pupils of church and cathederal schools. Piae Cantiones did not include music for the verses; these were to be sung to a well-known colloquial tune.
In AICSA circles, especially at IVs, Gaudete is usually sung with alternative and (usually) humourous verses (in English). A surprisingly large number of these begin with "Mary had a little lamb".
While the chorus is being sung, either someone will volunteer (by raising their hand) or be selected (by being pointed at by everyone else) to recite the next verse. The verse recitation is solo, and is either from a stock of "standard" AICSA verses or, for the more adventurous, made up on the spot. If the last word of the verse may be descibed in certain circles as "obscene", then the chorus starts by interrupting the last word - thus the questionable last word is never heard, but only alluded to.
A translation, by myself, is available.
Here are midi (computer music) files for you to download and listen to (If you're using Microsoft Windows, simply click on the link and they should play automatically. If you're not using Windows, I'm going out on a limb and assuming you're technically competent enough to figure things out for yourself....).
Also note that there are midi files of each individual voice part for each piece, so you can hear what each one sounds like - especially your own!
These midi files should give you a fair idea of what each piece - and each individual voice part - sounds like, especially if you're unfamiliar with reading music.
And for those that would like to dowload a viewable and/or printable copy of the score (HINT: most people will want the PDF file; don't try to view the Postscript file unless you know what you're doing):