The Capability Maturity Model Integration® framework was developed as a guide to applying good practices in process improvement, and this is the definitive reference for the "constellation" aimed at the development of products (there are companion volumes for product acquisition and service management).
The book starts with an overview of CMMI and how to use it. Of particular interest here are a number of "perspectives": short contributions on aspects of the history and application of CMMI, and a chapter containing helpful case studies and essays. These are generally the most readable and interesting parts of the book (except for a couple that are a bit too immersed in their own jargon).
The bulk of the content is a reference manual systematically describing the components of the model: the three Generic Goals, 13 Generic Practices, and 22 Process Areas. Each Process Area uses the same format, which makes it simple to follow, if not the most engaging read. Note that all this is freely available in electronic form from the Software Engineering Institute, except for a number of hints and tips.
This is the third edition, covering CMMI-DEV 1.3, which has attempted to streamline and clarify the model. New material includes quite a bit addressing the use of CMMI with agile methodologies - presumably in response to a perception (incorrect, the authors say) that they are in conflict.
Overall it's pretty dry (if you're allergic to acronyms, stay clear!), and abstract, but if you're after a good understanding of the model this is what you need. What it tries to do, it does well. If you want help applying it, though, you're likely to want something more concrete to go alongside it.
Disclosure: I received a copy of this book from the publisher in exchange for writing this review on behalf of CodeRanch.