Category mistakes are sentences such as 'Green ideas sleep furiously', 'Saturday is in bed', and The theory of relactivity is eating breakfast. Such sentences strike most speakers as highly infelicitous but it is a challenge to explain precisely why they are so. Ofra Magidor addresses this challenge, while providing a comprehensive discussion of the various treatments of category mistakes in both philosophy and linguistics. The phenomenon of category mistakes is particularly interesting because a plausible case can be made for explaining it in terms of each of syntax, semantics, and pragmatics-making it a fruitful case for exploring the relations between, and nature of, these three fundamental realms of language. Category Mistakes follows this division, discussing four types of accounts: the syntactic approach to the phenomenon, two distinct semantic approaches, and the pragmatic approach. Magidor argues that the first three ought to be rejected, and addresses the challenge by developing and defending a novel version of the pragmatic approach: the presuppositional account of category mistakes. Ofra Magidor is CUF Lecturer in Philosophy at the University of Oxford, and Fairfax Tutor and Fellow in Philosophy at Balliol College. She is also a member of the Faculty of Linguistics, Philology, and Phonetics at the University of Oxford. Her research focuses on Philosophy of Logic and Language and related issues in Metaphysics, Epistemology, and Philosophy of Mathematics. Previously, she was Junior Research Fellow at Queens college, Oxford. She holds a BPhil and DPhil in Philosophy from the University of Oxford, and a BSc in Philosophy, Mathematics, and Computer Science from the Hebrew University of Jerusalem.