 In recent decades, philosophers frequently refer to ‘intentionality’, roughly, that feature of beliefs, desires, and other mental states in virtue of which they are of or about something or more generally, possess content; contrary to what ordinary usage of ‘intentional’ might suggest, it is not limited to practical states such as intending to do something or acting intentionally. The currency of the technical term is due in large part to Edmund Husserl, who took it from his own teacher, Franz Brentano. In 1874, Brentano had proposed this feature as a criterion of the mental that could be used to demarcate psychology from the physical sciences, and he explicitly invoked medieval scholastic terminology (intentio, esse intentionale) as a way of reintroducing the notion. Brentano’s thesis about the criterion of the mental has had a checkered fate in philosophy. But interest in intentionality in its own right has continued unabated.