The topic of this article is the dependency or, maybe, the interdependency of rationality and self-knowledge. Here two questions may be distinguished, viz. whether being rational is a necessary condition for a creature to have self-knowledge, and whether having self-knowledge is a necessary condition for a creature to be rational. After a brief explication of what I mean by self-knowledge, I deal with the first question. There I defend the Davidsonian position, according to which rationality is, indeed, a necessary condition (...) for self-knowledge. In addition, I distinguish two aspects of rationality which I call basic and local rationality. After that I concentrate on the second question for the remaining larger part of this article. Here I proceed in two stages: first I examine whether self-knowledge is necessary for basic rationality, and then whether it is necessary for local rationality. (shrink)