Action Semantics is a novel approach to the formal description of programming languages. Its abstractness is at an intermediate level, between that of denotational and operational semantics. Action Semantics has considerable pragmatic advantages over all previous approaches, in its comprehensibility and accessibility, and especially in the usefulness of its semantic descriptions of realistic programming languages. In this volume, Dr Peter Mosses gives a thorough introduction to action semantics, and provides substantial illustrations of its use. Graduates of computer science or maths who have an interest in the semantics of programming languages will find Action Semantics a most helpful book.