The DSM is the main classification of mental disorders used by psychiatrists in the United States and, increasingly, around the world. Although widely used, the DSM has come in for fierce criticism, with many commentators believing it to be conceptually flawed in a variety of ways. This paper assesses some of these philosophical worries. The first half of the paper asks whether the project of constructing a classification of mental disorders that �cuts nature at the joints� makes sense. What is mental disorder? Are types of mental disorder natural kinds (that is, are the distinctions between them objective and of fundamental theoretical importance, as are, say, the distinctions between the chemical elements)? The second half of the paper addresses epistemic worries. Even if types of mental disorder are natural kinds there may be reason to doubt that the DSM will come to reflect their natural structure. In particular, I examine the extent to which the DSM is theory-laden, and look at how it has been shaped by social and financial factors. Ultimately, I conclude that although the DSM is of immense practical importance it is not likely to become the best possible classification of mental disorders.