This chapter concerns self-knowledge of our mental states, with a focus on how we know our own beliefs and intentions. It examines the agentialist approach to self-knowledge, which is driven by the idea that believing or intending on the basis of reasons is something that we DO, and hence involves agency. Agentialists maintain that, because beliefs and intentions are exercises of agency, self-knowledge of these attitudes differs fundamentally from self-knowledge of states that we simply undergo, such as sensations. Specifically, agentialists claim that self-knowledge of our attitudes is linked with our identity as rational thinkers, capable of believing and intending on the basis of reasons. This chapter outlines the agentialist approach to self-knowledge, and canvasses and assesses a range of agentialist accounts of how we know our own beliefs and intentions.