This chapter has only been an introduction to free software licensing issues. Although I hope it contains enough information to get you started on your own open source project, any serious investigation of licensing issues will quickly exhaust what this book can provide. Here is a list of further resources on open source licensing:
Understanding Open Source and Free Software Licensing by Andrew M. St. Laurent. Published by O'Reilly Media, first edition August 2004, ISBN: 0-596-00581-4.
This is a full-length book on open source licensing in all its complexity, including many topics omitted from this chapter. See http://www.oreilly.com/catalog/osfreesoft/ for details.
Make Your Open Source Software GPL-Compatible. Or Else. by David A. Wheeler, at http://www.dwheeler.com/essays/gpl-compatible.html.
This is a detailed and well-written article on why it is important to use a GPL-compatible license even if you don't use the GPL itself. The article also touches on many other licensing questions, and has a high density of excellent links.
Creative Commons is an organization that promotes a range of more flexible and liberal copyrights than traditional copyright practice encourages. They offer licenses not just for software, but for text, art, and music as well, all accessible via a user-friendly license selector; some of the licenses are copylefts, some are non-copyleft but still free, others are simply traditional copyrights but with some restrictions relaxed. The Creative Commons web site gives extremely clear explanations of what it's about. If I had to pick one site to demonstrate the broader philosophical implications of the free software movement, this would be it.