The International Summer School of Brain Research, on which this book is based, was organized by the Netherlands Institute for Brain research (NIBR), which has a rich history dating back to the beginning of the century.The focus of interest in this present volume of Progress in Brain Research are the few thousand neurons at the base of the hypothalamus that form the biological clock. Attention is focused on the mechanisms underlying the generation of circadian rhythmicity within our biological clock, which is still far from understood. Contributions originating from many disciplines give updates on the latest theories on the molecular and electrophysiological basis of the pacemaker mechanism, and the various approaches used in different species. Attention is also paid to the way the signal of the biological clock is transferred to the rest of the central nervous system. New data on the role of the suprachiasmatic nucleus and its impact on the functioning of the human being is presented. Altogether an excellent volume which will further the understanding of this elusive material.