Lawyers and programmers have at least one thing in common: their day-to-day work puts them in contact with issues that seem obscure and esoteric to the general public. That makes the terms of open source licenses doubly difficult to understand, but Lawrence Rosen does an admirable job explaining them in his book.
Rosen spends the next five chapters discussing the major open source licenses, spending an entire chapter on each type. The first type he covers is academic licenses, the BSD license being the most famous example. He talks about the GPL in chapter six, the Mozilla Public License in chapter seven, the Common Public License in chapter eight, and the OSL and the AFL in chapter nine.
Of all of the types of open source licenses, academic licenses are the least restricting. Software created under such a license can be used in almost any way; licensees can even take such software and use it later in proprietary products. Rosen strongly contrasts that with what he characterizes as the reciprocity bargain of the GPL, which he paraphrases as "You may have this free software on condition that any derivative works that you create from it and distribute must be licensed to all under the same license." It's because of the GPL, he explains, that we have two rather than one public commons of free commons. Software licensed under an academic open source license can be incorporated into a GPL project, but not vice versa.
Rosen also capably covers the political stance of the creators of the GPL, despite the fact that it is, he admits, irrelevant to the legal issues. Rosen also covers the Lesser GPL, designed to address the distribution of software libraries, something the regular GPL does not handle well. This is where the distinction we learned in chapter three about derivative works vs. collective works comes into play. He even touches on the economics of the GPL, since it specifies that derivative works must be licensed at no charge; as it turns out, there is an escape clause of sorts.
The other three chapters cover the continuing evolution of open source licenses, as programmers became savvier about the law; for instance, the MPL was one of the first licenses to explicitly grant a patent to licensees as well, and in fact deals with patents much more thoroughly than the open source licenses that came before it. Rosen has some good words for the CPL; unlike the GPL and BSD licenses, this much more modern open source license was actually created by lawyers (IBM's lawyers, to be exact), so its use of the language is particularly clear - in a legal sense, in any case. For example, "the words shall and must and may not always mean something mandatory, and the word may is always permissive." His discussion of the OSL and the ASL is more intricate in some ways than his earlier chapters, because those two licenses were intended to bridge the academic/reciprocal divide; still, he compares them point by point to each other and to other licenses, which helps in comprehension.