While Descartes’s Passions of the Soul has been taken to hold a place in the history to human physiology, until recently philosophers have neglected the work. In this research summary, I set Descartes’s last published work in context and then sketch out its philosophical significance. From it, we gain further insight into Descartes’s solution to the Mind--Body Problem -- that is, to the problem of the ontological status of the mind--body union in a human being, to the nature of body--mind causation, and to the way body-caused thoughts represent the world. In addition, the work contains Descartes’s developed ethics, in his account of virtue and of the passion of générosité in particular. Through his taxonomy of the passions and the account of their regulation, we also learn more about his moral psychology.