The papers in this volume offer a recollection of Leon Van Hove's rich life as a scientist from the "early days" to his latest interest. They also present, from several points of view, his action in favor of scientific collaboration across national and international boundaries and of the cultural integration of Europe where he acted as a leader in several institutionsparticipation of many distinguished scientists and some top officials of the European Community. They are also a tribute to his figure as a scientist and to his important contributions to many areas of mathematical and theoretical physics, from statistical mechanics to field theory and multiparticle production.