Organisms are obviously adapted, but in what ways are they optimal, and why does it matter? These are complex questions that have been debated from various points of view for years, so I approached this collection of essays with a mixture of hope and dread. The twelve chapters differ greatly in focus and style; collectively they touch on issues and facts from a wide range of fields including philosophy and history of science, phylogenetics, population genetics, game theory, physiology, behavior, and ecology; they cohere as a group only in their general relationship to the theme of the volume, and they reach no consensus. This unruliness is a virtue, in my opinion, because there are no simple answers to the central questions. The chapters frequently illuminate each other (if obliquely), and, although strong opinions are often expressed, each makes an able, honest, and thoughtful attempt to sort out some aspects of the roles played by concepts of adaptation and optimality in biological research. I found the book very stimulating. It will undoubtedly anchor the reading lists of many graduate seminar courses over the next few years. However, there are holes that will need to be filled from other sources, and I recommend reading the chapters in an order almost reverse that in which they appear in the volume. The penultimate chapter by Peter Godfrey-Smith (‘‘Three kinds of adaptationism’’) argues that the debates have raged so long and hot in part because three distinct issues have been lumped together under the term ‘‘adaptationism’’: the first is empirical adaptationism (the claim that selection in fact tends to dominate other evolutionary processes, at least where significant fitness differences are at stake); the second is explanatory adaptationism (the claim that apparent organismal design and fit to environment are evolutionary biology’s central problem and therefore that natural selection and adaptation are the central answer); and the third is methodological adaptationism (the claim that useful hypotheses are often discovered by asking how selection might, in principle, optimize some trait of interest). Each of these ‘‘kinds’’ or ‘‘dimensions’’ of adaptationism is logically independent of the other two, and each can be qualified or weakened in various ways, so there are many different ‘‘adaptationist’’ positions that individual biologists might (and do) represent. For example, it is possible and logically consistent to be (1) very optimistic about the near optimality of most ecologically important traits in real organisms (1 empirical adaptationism) and (2) zealously committed to the primacy