In this thesis I consider the problem of the distinctiveness of knowledge of our own mental states and attitudes. I consider four influential approaches to this problem: the epistemic approach, the "no reasons view," the neo-expressivist approach and the rational agency approach. I argue that all of them face serious problems. I further argue that many of these problems are connected with the lack of fine-grained enough classification of the entities with respect to which we have self-knowledge. I suggest such a classification, distinguishing passive occurrent mental states, mental actions and standing attitudes, and argue that we should treat each of these categories separately for the purpose of explaining self-knowledge of them. I discuss in detail self-knowledge we have with respect to two of these categories: standing attitudes and mental actions. On my account self-knowledge of standing attitudes stands in a derivative relation to self-knowledge of other kinds. In my discussion of self-knowledge of mental actions I establish that we have a distinctive non-observational kind of self-knowledge and show some specific characteristics of this kind of self-knowledge. In the end I attempt to relate self-knowledge of mental actions to practical knowledge in the ordinary sense of skill.