This paper is an exploration of the Thomistic vice of despair, one of two vices opposed to the theological virtue of hope. Aquinas's conception of despair as a vice, and a theological vice in particular, distances him from contemporary use of the term "despair" to describe an emotional state. His account nonetheless yields a compelling psychological portrait of moral degeneration, which I explain via despair's link to its "root," the capital vice of sloth. Cases in which sloth and its offspring vices progress into full-fledged despair raise intersecting issues about whether and how despair might be remediable. I conclude by considering puzzles regarding despair's disordered effects on the intellect and will and weighing three possible means of remedying it.