The libertarian theory of free will combines 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 involve exercises of free will---'free actions,' for short. While remaining neutral on this negative thesis, Aspects of Agency 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 so instigated. The bulk of Mele's work is a masterful defense of a positive libertarian thesis against objections to theses of its kind. Aspects of Agency includes solutions to problems about luck and control that are widely discussed in the literature on free will and moral responsibility. 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.