This book, with an overview introduction by Kenneth J.Arrow, is the first volume of the proceedings of the World Economic Congress held in Athens, Greece, in August/September 1989 under the auspices of the International Economic Association. It contains in Part 1 lectures from the plenary session by distinguished world economists. Part 2 contains surveys and reflections on various aspects of markets in equilibrium. Part 3 is concerned with normative criteria for economic policy within the framework of welfare and social choice theory.