There is no perfect conservaton biology textbook, but this one is probably the best all-around choice for a general introduction to the field. I've just switched to this textbook for my undergraduate Conservation Biology class. I don't know what the 3rd edition was like, but the 2006 4th edition seems very nicely organized and well-written. I've tried 2 other texts for this course and found Hunter & Gibbs to be too oversimplified, while Groom et al. is too advanced for most undergraduates. Groom et al. is a fantastic reference for a professional or grad student, but is just too overwhelming for your average sophomore bio major. Anyway, Primack's 4th edition hits the middle ground exactly right - a lot of good detail, all the key vocabulary, decent coverage of recent developments in the field, clearly written, nice figures, but not too overwhelming. It's organized in 6 major sections: (1) biodiversity (what & where it is), (2) why we should care, (3) why it's vanishing, (4) population biology (how to keep a small pop'n going), (5) practical solutions (reserve design, restoration ecology etc.), and (6) human society. I plan to supplement it with outside readings & a case-study popular book or two, probably Kurlansky's "Cod" for a look at how human history, culture & economics can combine to gradually drive a species under, and Bodsworth's "Last of the Curlews" (the edition with the beautiful illustrations by T.M.Shortt) just for emotional impact and sheer beauty.