This book helps to organise the diverse landscape of agent-based systems by applying formal methods to provide a defining and encompassing agent framework. The Z specification language is used to provide an accessible and unified formal account of agent systems and inter-agent relationships. In particular, the framework precisely and unambiguously provides meanings for common concepts and terms for agent systems, enables alternative agent models and architectures to be described within it, and provides a foundation for subsequent development of increasingly more refined agent concepts. It describes agents, the relationships between them and the requisite capabilities for effective functioning in multi-agent systems, and is applied in different case studies. In the second edition the authors have revised and updated the existing chapters of the book to respond to advice from readers of the first edition, to add references to recent work in agent systems, and generally to bring the content up to date. They have extended the introduction and conclusions chapters to include a better review of the field and the current state-of-the-art. This new edition features chapters on agent interaction and norms, and outlines an implementation framework. The book will appeal equally to researchers, students and technologists interested in intelligent agents and multi-agent systems. Comments from experts in the field: An excellent book that lays out a clear conceptual framework for studying and analysing agent-based systems. Nick Jennings Mark d'Inverno and Michael Luck have, over the last six or seven years, been at the forefront of European research in agent systems. This book poses some important foundational questions about agents and their interactions in multi-agent systems and answers them in a coherent and convincing way. It's an extremely valuable contribution to the field. Michael Georgeff It is undoubtedly a clear and most comprehensive attempt to describe agent-based systems in a unified manner. Simon Parsons