The theme is official, then - duets and trios. For the purpose of counting whether something is within the theme: 1) There need to be either two or three lead vocalists on your song. A rap section counts as a lead vocal. A person singing the lead on a verse or the hook counts as a lead vocal. Background vocals do not count. 2) If the two or three vocalists are officially credited, then great - but it's not necessary as long as (1) is satisfied. 3) The two or three vocalists can be within the same band or they can be artists who don't normally collaborate - either is fine. 4) If an act is the sort of act that generates tons of discussion around Popjustice, there's a good chance that even their most obscure track will get vetoed - but, as @Eric Generic pointed out, an obscure song by a fairly well-known act could work (and is better than a well-known song by any artist). However, there's no limit on the number of backups you can have, so if you send me a song and it gets vetoed you can always send in another. I'll open the thread in the next week or so, but if you have any questions ask me here or by PM. Feel free to submit stuff now - one person already has!