This book uses Sperber and Wilson's Relevance Theory to show how evidential expressions can be analysed in a unified semantic/pragmatic framework. The first part surveys general linguistic work on evidentials, presents speech-act theory and examines Grice's theory of meaning and communication with emphasis on three main issues: for linguistically encoded evidentials, are they truth-conditional or non-truth-conditional, and do they contribute to explicit or implicit communication? For pragmatically inferred evidentials, is there a pragmatic framework in which they can be adequately accounted for? The second part examines those assumptions of Relevance theory that bear on the study of evidentials, offers an account of pragmatically inferred evidentials and introduces three distinctions relevant to the issues discussed in this book: between explicit and implicit communication, truth-conditional and non-truth-conditional meaning, and conceptual and procedural meaning. These distinctions are applied to a variety of linguistically encoded evidentials, including sentence adverbials, parenthetical constructions and hearsay particles. This book offers convincing evidence that not all evidentials behave similarly with respect to the above distinctions and offers an explanation for why this is so.