This paper develops an account of the nature of imagination as a discrete mental process underpinned by a specialised neural and computational architecture. The account integrates evidence from cognitive neuroscience and developmental psychology with philosophical arguments about the nature of imagination. We situate the account against other philosophical accounts and apply it to the understanding of some puzzling phenomena: delusion, pretence and self-deception. We argue that many of the puzzling features of these phenomena arise because they are analysed with a doxastic framework. When the role of imagination in these cases is properly understood these puzzles become more tractable.