The distinction between occurrent and non-occurrent mental states is frequently appealed to by contemporary philosophers, but it has never been explicated in any significant detail. In the literature, two accounts of the distinction are commonly presupposed. One is that occurrent states are conscious states. The other is that non-occurrent states are dispositional states, and thus that occurrent states are manifestations of dispositions. I argue that neither of these accounts is adequate, and therefore that another account is needed. I propose that occurrent states are active states.