Creative Commons licensing arose to expand the range of creative works available for others to build upon legally and to share. Many authors really want their works to be redistributed for free in venues such as Cooks Source, but they want to make sure attribution is given, and often want to prevent their work from being altered or chopped into pieces. Others want to make sure that if their work is altered or somehow improved, the altered or improved version will also be available for free. Sometimes, authors are happy to have their works reused non-commercially, but want to keep their works from being commercially exploited without permission. Creative Commons licenses give authors the tools they need to accomplish these goals.
The different licenses available from Creative Commons are designated with a special mark, with added code letters that indicate the features invoked by the rights holder. For example, the "Attribution-ShareAlike" license is denoted by the letters "CC BY-SA" and the mark shown. This license requires attribution as to the author of the work, and the ShareAlike features bind the licensee to share any modifications or improvements.
It's important to note that in the Creative Commons licenses, the owner of the copyright does not give up ownership of the work. The owner is free to re-license the work under any terms they desire, and can still sue people who infringe on the copyrights. The owner licenses the work to the user, who accepts the license as a condition of use. The user can in turn distribute the work along with a copy of the license to other users, who accept the terms of the same license from the copyright owner as a condition of their use.
Creative Commons licensing is now widely used for free e-books distributed on the web. Perhaps the best known e-books using CC are the works of Cory Doctorow, a blogger, science fiction author and advocate for copyright law reform. It's also used for contributions to Wikipedia -- http://www.wikipedia.com -- and is supported by Flickr -- http://www.flickr.com -- for use in photos.
