"Carl F. Craver and Lindley Darden eloquently describe the discovery of mechanisms and reasoning about them and show how mechanisms provide an integrative way of understanding the unity of biology. This book ranges across many areas of biology and is highly readable, with rich examples and a minimum of philosophical jargon. It substantially advances the philosophy and history of science, and can seriously help biologists to understand their own work." (Paul Thagard, University of Waterloo)"