“Crystallization, as applied to proteins, was long held in high esteem, but hardly considered science.” I quote from the preface to Alexander McPherson's new survey of the field, Crystallization of Biological Macromolecules. Years ago, McPherson's previous monograph (Preparation and Analysis of Protein Crystals, 1982, Wiley) introduced me to the subject. The growth of knowledge about protein crystallization in the past 17 years is vividly illustrated by comparison of the two books. The slim old volume contained a single chapter on experimental procedures for protein crystallization. In contrast, the 1999 book has three chapters on experimental issues, plus several chapters that review the emerging understanding of the physical chemistry of macromolecular crystallization.