The purpose of the preface is to explain the book's objectives and how to use it; give warnings, disclaimers, and the like.* The main objective of Protein and Peptide Analysis by Mass Spec- trometry is quite straightforward-to present authoritative, up-to-date, and practical accounts of the use of mass spectrometry in the analysis of pep- tides and proteins. How to use it? Every reader will have their own particular interests and will surely be drawn toward the chapters that cover these interests. Within the remaining chapters, however, techniques are described with analytical possibilities that such a reader can then only guess at. So, read the book fully. Again, as is customary in the Methods in Molecular Biology series, the chapter format (Introduction, Materials, Methods, and Notes) allows the authors to introduce the techniques, to explain their relevance and applicability, and, above all, to provide detail-detail that represents each author's accumulated experience and enables the reader to use and benefit from these methods. So, read the book fully, and read it diligently. Warnings and disclaimers: Mass spectrometry today offers the pro- tein chemist ready access to a wealth of information that is otherwise avail- able only with great difficulty, or perhaps not at all. With this goal in sight, any warnings and disclaimers will almost surely be ignored. So, a warning anyway; the use of mass spectrometry might be habit forming.