Choral Public Domain Library

La, la, la l'oysillon du bois by Jean Mouton

I've been trying to find sheet music for it online and I've only found a website in French that appears to have it for sale. I'm guessing it is copyrighted?

Any music by Jean Mouton is out of copyright, but the edition you found may be (and probably is) copyright.

Chuck

Since Jean Mouton died in 1522, the piece itself would be in the public domain, pretty much throughout the world. The particular edition you see for sale may or may not be subject to copyright, depending upon many things (some of which are quite variable from country to country). In the United States, there has to be some sort of creative editorial input for a copyright to be valid; merely mechanical transcriptions of public domain works are not themselves copyrightable. (Of course, some forms of transcription, taking the term a bit broadly, are creative works in themselves and thus copyrightable.) Some other countries provide some copyright or similar protection for editions of public domain works. How these differing laws all relate together internationally gets to be rather complicated, to say the least.