This book argues against the mainstream view that we should treat propositional attitudes as internal states, suggesting that to treat beliefs as things of certain sort (i.e. to reify them) is a mistake. The reificatory view faces several problems that the non-reificatory view avoids, and it is argued the non-reificatory view is more faithful to the everyday concept of belief. There are several major reasons why it might be thought that a reificatory approach to mental states is nevertheless unavoidable, but this book attempts to show that none of these reasons is at all convincing; in each case, the evidence is consistent with a non-reificatory view.