The concept of species has played a central role in both evolutionary biology and the philosophy of biology, and has been the locus of a number of books in recent years. This book differs from other recent collections in two ways. It is more explicitly integrative and analytical, centering on issues of general significance such as pluralism and realism about species. It also draws on a broader range of disciplines and brings neglected cognitive, anthropological, and historical dimensions to philosophical debates over species. The chapters are organized around five themes: unity, integration, and pluralism; species realism; historical dimensions; cognitive underpinnings; and practical import. The contributors include prominent researchers from anthropology, botany, developmental psychology, the philosophy of biology and science, protozoology, and zoology.