Center for the Study of the Public Domain
It's useful for anyone studying copyright issues to examine discussion of the public domain. Those works not protected by exclusive copyright are in the public domain. In other words, they are available for copying without permission from the creator. This happens if the author explicitly offers works for the public domain or when copyright expires.
I found a link to this site from the Union College page on copyright, and it looks like it has a wealth of links to scholarship, projects and events.
My favorite pointer at the moment: Jerome H. Reichman (with Keith E. Maskus), The Globalization of Private Knowledge Goods and the Privatization of Global Public Goods
Duke University Law School
Center for the Study of the Public Domain
http://www.law.duke.edu/cspd/articles/reichman.pdf