This book offers an examination of functional explanation as it is used in biology and the social sciences, and focuses on the kinds of philosophical presuppositions that such explanations carry with them. McLaughlin gives a critical review of the debate on functional explanation in the philosophy of science that has occurred over the past fifty years. He discusses the history of the philosophical question of teleology, and provides a comprehensive review of the postwar literature on functional explanation. The book provides a sophisticated and detailed Aristotelian analysis of our concept of natural functions, and offers a positive contribution to the ongoing debate on the topic.