In December 2006, the National Academy of Sciences sponsored a colloquium (featured as part of the Arthur M. Sackler Colloquia series) on Adaptation and Complex Design to synthesize recent empirical findings and conceptual approaches towards understanding the evolutionary origins and maintenance of complex adaptations. Darwin’s elucidation of natural selection as a creative natural force was a monumental achievement in the history of science, but a century and a half later some religious believers still contend that biotic complexity registers conscious supernatural design.In this book, modern scientific perspectives are presented on the evolutionary origin and maintenance of complex phenotypes including various behaviors, anatomies, and physiologies. After an introduction by the editors and an opening historical and conceptual essay by Francisco Ayala, this book includes 14 papers presented by distinguished evolutionists at the colloquium. The papers are organized into sections covering epistemological approaches to the study of biocomplexity, a hierarchy of topics on biological complexity ranging from ontogeny to symbiosis, and case studies explaining how complex phenotypes are being dissected in terms of genetics and development.