An attempt to provide a conceptual framework within which various key aspects of communication can be described, and to present a formal language based on modal logic to formulate these descriptions. There are chapters on signs and signalling, the presentation of the formal language, a discussion of some features of communication situations (including notions like truthfulness, trust, Moore's paradox, informing and asserting, intentions, etc.), the description of non-indicatives (their relation to truth conditions, performatives, the logic of imperative inference, etc.), on intention-dependent evidence, and on the `double bind' (i.e. how to describe the language of schizophrenics).