This thesis argues for a conjunctive account of knowing, one according to which, the condition picked out by our ordinary uses of the verb "knows" is the conjunction of a mental and a non-mental component. I argue for a specific version of this account, one that identifies rational belief as the mental component of knowing. The account sheds light on the relations between three important epistemic concepts: knowledge, rational belief, and evidence. It also fixes the "boundary" between the mental and the non-mental in a way that undermines certain, otherwise, plausible skeptical arguments against the possibility of rational belief. In both cases, the account offers substantive answers to important questions in epistemology and philosophy of mind and brings in focus the points of connection between the two fields.