In this thesis I give a response to external world scepticism. I first argue that scepticism arises when we accept that it is an empirical question whether I am in a sceptical scenario, that is, a scenario in which my beliefs are coherent, and yet my empirical beliefs are false. The idea that it is an empirical question whether I am in a sceptical scenario gets its plausibility from the realist claim that our empirical beliefs have an objective subject matter. I then attempt to give a response to scepticism that is compatible with this realist claim. Three promising responses to scepticism are considered, but are found to be inadequate. Seeing why these responses are inadequate helps us to appreciate some of the conditions on an adequate response to scepticism. By drawing on the work of Donald Davidson I develop a response to scepticism that is compatible with the realist claim, and that meets these conditions. According to this response, when we get clear about the concept of belief we see that sceptical scenarios are a conceptual impossibility. Thus, just as it is not an empirical question whether I am a married bachelor, it is not an empirical question whether I am in a sceptical scenario, and the argument for scepticism breaks down.