René Descartes’ conception of the human will has important implications for his conception of human beings as rational and moral agents. Specifically, the will plays a significant role in his views on what control we have over our beliefs; what kind of freedom we enjoy; how our emotions affect our actions, and how we can moderate our emotions. I explore these issues in three contexts that arise throughout Descartes’ corpus, from his earliest significant work, Rules for the Direction of the Mind (the Regulae, 1619-1628), to his last published work, The Passions of the Soul (1649). I begin with the question of why Descartes construes judgment as an operation of the will in the Meditations. This is a change in view from the Regulae. I argue that to understand this change, we need to consider his conceptions of error and activity in the Regulae. I trace the development in his philosophical views about error and activity from the Regulae to the Meditations and show that these commitments underpin his mature theory of judgment. I then turn to Descartes’ conception of freedom in the Fourth Meditation. Descartes’ conception of the will, I argue, figures centrally in his conception of freedom. I show that Descartes holds that freedom is compatible with determination and consists in the power of the will to determine itself. I show, further, that Descartes’ later correspondence helps to clarify and unify his characterization of freedom in the Fourth Meditation: freedom is proportional to the ease of self-determination. Lastly, I consider Descartes’ conception of the relationship between the will and the passions of the soul (the passions). I begin by addressing how the passions affect the will, and I argue for a “bifurcated” approach to the function of the passions. This interpretation holds that the passions affect the will differently depending on what kind of volition results—volitions involved in action or volitions involved in judgment. I then discuss several ways in which Descartes conceives of the passions as problematic. I conclude by exploring three means Descartes prescribes for controlling them: habituation, indirect control, and the regulation of desire.