Every language has a way of saying how one knows what one is talking about, and what one thinks about what one knows. In some languages, one always has to specify the information source on which it is based—whether the speaker saw the event, or heard it, or inferred it based on something seen or on common sense, or was told about it by someone else. This is the essence of evidentiality, or grammatical marking of information source—an exciting category loved by linguists, journalists, and the general public. This volume provides a state-of-the art view of evidentiality in its various guises, their role in cognition and discourse, child language acquisition, language contact, and language history, with a specific focus on languages which have grammatical evidentials, including numerous languages from North and South America, Eurasia and the Pacific, and also Japanese, Korean, and signed languages.