The Creative Commons <http://creativecommons.org/> family of copyright licences has become very popular for artworks, documentation and all kinds of creative works generally. But there are different kinds of Creative Commons (CC) licences, with additional qualifications, namely “BY” (attribution required, i.e. give credit to the creators), “SA” (sharealike or “copyleft”, i.e. if you redistribute, do it on the same terms it was given to you), “NC” (non-commercial use only) and “ND” (no derivatives--i.e. modified versions--allowed), and certain combinations thereof. These qualifications divide the CC licences into two categories: Free and non-Free. The non-Free CC licences are those including NC or ND or both, while the Free ones are the rest: * CC0 -- effectively public domain * CC-BY -- distribution with attribution required * CC-BY-SA -- sharealike distribution with attribution If you want to promote sharing and contribute to Free Culture, stick to these three licences. In particular, here <http://freedomdefined.org/Licenses/NC> is a detailed discussion of the NC restriction, and why it is such a bad idea. Most people who stick an NC licence on their work think in terms of preventing big commercial outfits from “ripping them off”. However, this licensing restriction may not achieve what you think it does, particularly since it is often unclear what constitutes “commercial” use anyway.