Philosophers have traditionally assumed that the difference between active and passive movement could be explained by the presence or absence of an intention in the mind of the agent. This assumption has led to the neglect of many interesting active behaviors that do not depend on intentions, including the "mindless" actions of humans and the activities of non-human animals. In this book Jones offers a broad account of agency that unifies these cases. The book addresses a range of questions, including: When are movements properly attributed to whole agents, rather than to their parts? What does it mean for an agent to guide its action? What distinguishes agents from other complex systems? What is the relationship between action and adaptive behavior? And why might the study of living systems be the key to understanding agency? This book makes an important contribution to current philosophical debate on the nature and origins of agency. It defines action as a uniquely biological process and recasts human intentional action as a specialized case of a broader and more common phenomenon than has been previously assumed. Uniting findings from philosophy, cognitive science, psychology, biology, computer science, complexity theory and ethology, this book will be of interest to students and scholars working in these areas.