These 14papers were presented to a conference of the IEA held at the International Centre for Economic Research, Turin. Four areas are identified in which theoretical and empirical developments are discussed for the fuller understanding of personal (as opposed to collective) behaviour with economic objectives: rational choice and associated problems of logic rationality as explained by game theory experiments to elucidate rational behaviour and alternative treatments of rationality in decision making theory. The preface by Nobel Laureate Kenneth Arrow traces the evolution of concepts of economic rationality from the start of this century.