Economics, dealing with mental processes of decision makers is part of cognitive science; conversely, cognitive science, faced with constraints on information processing, is part of economics. In July 1990, the Cecoia 2 conference was organised in Paris to further explore the connections between the two. The papers presented in this volume illustrate this truly interdisciplinary research intertwining social and cognitive sciences. Three main topics are represented: agent’s mental representation when facing complex uncertainty; agent’s computational constraints leading to bounded rationality; agent’s learning and evolution in an imperfectly known environment.