This book is dedicated to Marek Sergot, Professor of Computational Log at Imperial College London, on the occasion of his 6oth birthday. Professor Sergot's scientific work covers many different fields. He has developed a series of novel ideas and formal methods bridging areas including artificial intelligence, computational logic, philosophical logic, legal theory, artificial intelligence and law, multi-agent systems and bioinformatics. By combining his background in logic and computing with his interest in law, deontic logic, action and related areas, and by applying to all his ability to understand the subtleties of social interaction and normative reasoning, Professor Sergot has opened up new directions of research, and has been a reference, an inspiration and a model for many researchers in the fields to which he has contributed.The Festschrift includes several reminiscences and introductory essays describing Professor Sergot's achievements, followed by a series of articles on logic programming, temporal reasoning and action languages, artificial intelligence and law, deontic logic and norm-governed systems, and logical approaches to policies.