The chapter discusses Epicurus’s notions of voluntary action, moral responsibility, and the swerve of atoms. I examine the ancient evidence first, including Epicurus’s Letter to Herodotus, Letter to Menoeceus, and On Nature Book 25, and Lucretius, On the Nature of Things 2.216–93. I argue that the evidence, especially the Lucretius passage, favors the interpretation that Epicurus believed the swerve of atoms plays a role in every voluntary action of living creatures. But I also take seriously the views of scholars who disagree with this position. Indeed, viewed from one perspective, the lack of scholarly consensus on the role of the swerve in Epicurus’s analysis of voluntary action and moral responsibility provides strong justification for thinking that the precise role that the swerve played is irrecoverable from the ancient evidence available to us. Viewed from another perspective, however, the lack of scholarly consensus, combined with the plausibility of a number of different views about the role the swerve may have played in Epicurus’s system, points to a solution of a different kind. Rather than maintaining that the swerve played a single role in Epicurean psychology, it may be more productive to suppose that it could have played a number of roles. Once Epicurus posited the swerve, he seems to have used it in a number of aspects of his psychology and account of voluntary action and moral responsibility.