Lawrence Lessig on Creative Commons:
Creative Commons offers free copyright licenses to artists and creators. The purpose of the license is to enable the artist or creator to mark his or her copyrighted work with the freedom he or she intends the work to carry. Those “freedoms” are the exclusive rights that copyright grants the copyright holder which the law permits the copyright holder to waive. The design of the system is to be automatic. No contract, or meeting of the minds, is intended. It is simply a license that says “if you use my copyrighted work in ways that would otherwise infringe my exclusive rights, I won’t sue you if you have abided by this license.” (The law makes everything ugly, but anyway, that’s what it does.)