Human beings are beings that act. But what are actions and what are reasons for action? Without assuming prior knowledge of the discipline, Ralf Stoecker uses these questions to present the essential topics of modern philosophy of action: reasons for action, rationality and irrationality, responsibility, and the difference between action and mere behavior. These topics have significant consequences for different areas of philosophy, particularly contemporary problems in applied ethics like the difference between killing and letting die or the limits of justified warfare. The book is directed equally to students, professional philosophers, and those interested in the topic from other areas of study.