Libertarianism about free will is the conjunction of a negative thesis and a positive thesis. The negative thesis is that free will is incompatible with determinism. The positive thesis is that there are actions that are or involve exercises of free will—free actions, for short. While remaining neutral of the negative thesis, this book develops a detailed version of the positive thesis that represents paradigmatically free actions as indeterministically caused by their proximal causes and pays special attention to decisions caused in this way. The bulk of the book is a defense of this thesis against popular objections to theses of its kind. This defense includes solutions to problems about luck and control that are widely discussed in the literature on free will and moral responsibility. Various key concepts are clarified, including complete control, direct control, and its being up to an agent what is decided; and it is argued that free will may be accommodated without invoking agent-causation. The seven chapters on free will are preceded by an introductory chapter and three chapters on central issues in the philosophy of action that bear on standard treatments of free will—deciding to act, agents’ abilities, and commitments of a causal theory of action explanation.