That X-ray crystallography relies on crystals is common sense, but production of diffraction-quality crystals of macromolecules is by essence unpredictable and is therefore one of the last problems not entirely under control in biocrystallography. This explains why the crystallization of proteins and other biomacromolecular systems was often considered by crystallographers as an ‘art’ or a subtle and esoteric implementation of recipes rather than a rational scientific undertaking. However, there is an inverse tendency, advocated by an increasing number of scientists, that fights against such an irrational view.The novel book by Alexander McPherson is a robust contribution to the field of biocrystallography, showing that the complexity of macromolecular crystallization can be understood and often controlled. In the course of its ten chapters, the book presents the advances in the field and discusses the novel trends that are transforming macromolecular crystallization from empiricism to a true science. The author is ambitious — not only did he aim to cover the difficult field of biomacromolecule crystallization, as such, but also the related aspects of biochemistry, structural biology, and physics. Altogether he succeeded, although at the cost of certain simplifications for the latter sister disciplines. The book contains an extensive reference list and an iconography highlighting not only the beauty and diversity but also the ‘pathologies’ of macromolecular crystals; it is written by one of the experts in the field and is intended for a large readership. First, it will give biologists and biocrystallographers a comprehensive introduction to the physics underlying any crystallization process and its application to macromolecules. Rather than give formal descriptions of current crystal growth theories, the author has chosen to qualitatively explain their principles and to show how they actually apply in the macromolecular field. This text will also interest physicists, who will find basic information about proteins that is often lacking in specialized literature on crystal growth, in particular what concerns their architecture, physical characteristics, how they are purified, and, most important, the features that make proteins different from other materials. Information about nucleic acids, nucleoprotein complexes, and membrane proteins is more scarce, but the author has chosen to emphasize globular proteins for which the physical chemistry of their crystallization is the best established. An essential part of the book is devoted to methodological and practical aspects of protein and nucleic acid crystallization. It will be an especially invaluable resource for beginners, and the Appendix, with practical information on buffers, crystallizing-agent solutions, recipes for crystallizing several test proteins, and basic protocols for protein analysis, will help them to design their experiments.In Chapter 1, McPherson sketches the main characteristics of macromolecular crystals and outlines the history of the field. Work in the field started in 1840 and culminated in its first phase with the crystallization of tobacco mosaic virus and the work of Sumner on enzymes, before being gradually influenced by the diffractionists after 1930. Chapter 2 is a survey of the basic principles of macromolecular structure and the application of X-ray crystallography. It is dominated by the protein world and gives only a few indications on nucleic acid architectures. The catalogue of macromolecular shapes will remind physics-oriented readers that biological macromolecules are not simple spherical items, as they are often considered in crystal growth theories. Chapter 3 deals with the current biochemical purification and characterization methods of proteins, but is lacking in information about chemical and molecular biology techniques for macromolecule production.The next four chapters are pivotal. Chapter 4, on physical and energetic principles, explains what supersaturation, solubility and a phase diagram are, and discusses crystallization as a phase transition and/or a self-assembly process involving packing interactions. Chapter 5 is essentially practical; it describes the methods currently used by structural biologists to grow crystals, lists the properties of crystallization agents and discusses how supersaturation can be reached. Chapter 6 shows how physical, chemical, and biochemical factors influence protein crystal growth and discusses in great detail the importance of ‘purity’ in crystallogenesis. Strategies and special approaches for growing crystals are described in Chapter 7. Here, the author gives a number of pertinent recommendations for choosing the best crystallization strategy, critically discussing advantages and difficulties with screening methods and seeding procedures; he also explains what cessation of growth is and how crystals can be manipulated and modified.The last three chapters of the book present the latest developments in the field. The effects of impurities on crystals, how they generate defects and what the defects are, together with methods to characterize crystal quality, are outlined in Chapter 8. The relationship between phase transition and nucleation and the mechanisms of crystal growth are presented in Chapter 9. Chapter 10 deals with crystal growth in unique environments. Microgravity crystallization, often dismissed with fallacious arguments in the past, is critically discussed and the most recent experimental evidence showing positive effects on maximum resolution and mosaicity are presented. Other specialized methods are also highlighted, such as crystallization under oil, in capillaries, on membranes, and in gels, the last case deserving to be better known because of its great potential for improving crystal quality. Chapter 10 also contains two attractive sections on industrial crystallization and on protein crystals as they grow in vivo.In contrast to former surveys that covered a field still in its infancy, and thus frustrated many readers because there were too few achievements to report, the present second-generation book should please them. It shows that conclusions on crystallization behaviours no longer quasi-exclusively originate from studies on the test-case protein lysozyme, but come also from the crystal growth of a broad range of other proteins and even from viruses and tRNA. It shows further how techniques like atomic-force microscopy, light scattering, interferometry, and diffraction methods used to assess crystal perfection have transformed the discipline into a true science.The question still remains: ‘Can diffraction-quality crystals of any protein be grown on demand?’ The answer, obviously, is still no because of the multiparametric nature of the crystal growth process, and most likely in the future many crystals will still be obtained by empirical means. However, McPherson's book should convince readers that the mysteries surrounding biomacromolecule crystallization are gradually being solved and that rational remedies can be brought to difficult crystallization problems. It should also encourage beginners to enter into the crystallization ‘game’ without preconceptions. Rather than simply being a compilation of recipes, this book is a nice mix of practical and theoretical considerations that will guide the experimentalist to find the adequate crystallization conditions for macromolecules of increasing structural complexity. Finally, and perhaps of most important practical consequence, this text provides a panel of strategies for improving the quality of crystals and consequently obtaining X-ray structures of better quality.