The essays appearing in these two volumes are based on Keynote (Vol. 1) and State of the Art (Vol. 2) Lectures delivered at the XXVth International Congress of Psychology, in Brussels, July 1992. The Brussels Congress was the latest in a series of conferences which are organized at regular intervals under the auspices of the International Union of Psychological Science (IUPsyS), the main international organization in the field of Scientific Psychology. The first of those meetings took place in Paris in 1889. An important function of the International Congresses is to promote communication...