The recent spread of 'structuralist' writing has been hailed as the dawn of a new age and condemned as an intellectual disaster but, like all fashionable diseases, it is more talked about than understood. Edmund Leach's new book is designed for the use if teaching undergraduates in anthropology, linguistics, literary studies, philosophy and related disciplines faced for the first time with structuralist argument; it provides the prolegomena necessary to understand the final chapter of Levi-Strauss's massive four-volume Mythologiques. The objective is complex, the manner simple. Some prior knowledge of anthropological literature is useful but not essential; the principal ethnographic source is the Book of Leviticus; this guide should help anyone who is trying to grasp the essentials of 'seminology' - the general theory of how signs and symbols come to convey meaning. Although, in essence, a textbook, substantial portions of the argument are here presented for the first time; thus Section 16 contains an innovating contribution to general incest theory, and the analysis of the logic of animal sacrifice presented in Section 18 is an advance on anything previous published on this theme. The author's core thesis is that: 'the indices in non-verbal communication systems, like the sound elements in spoken language, do not have meaning as isolates, but only as members of set'; the book's special merit is that it makes this kind of jargon comprehensible in terms of our everyday experience.