The present volume of Progress in Brain Research contains the proceedings of a Symposium entitled Cerebellar Modules: Molecules, Morphology and Function, which was held to mark the retirement of Jan Voogd as chairman of the Department of Anatomy at the Erasmus University of Rotterdam. The contributions of leading cerebellar scientists representing a variety of disciplines focussed around the issue of the cerebellar modular compartmentalization, the intriguing composition of which has for many decades been the driving force behind Voogd's extraordinarily detailed anatomical analyses. The first section of the book, Development, concentrates on the genetic basis of different aspects of compartmentalized development including a most important contribution on the postnatal development of the climbing fiber system. Gene expression is also an important element in the next section, Interneurons, which provides striking new data and hypotheses on the functional anatomy of granule cells, Golgi cells and unipolar brush cells. Particularly interesting are several contributions that offer a novel view on parallel fiber function. The section Modules and Circuits provides a number of state-of-the-art analyses using electrophysiological, and classical and transneuronal virus tracing techniques. The emphasis lies on the olivocerebellar circuits and the oculomotor system The final section, Models and Learning, offers an insight into the progress on the mechanisms and network organization of adaptation and learning, not only in classical paradigms like oculomotor and eye blink responses but also in studies linking gene expression to behavioral paradigms The editors are confident that the exciting data and concepts collected in this volume will strengthen the multidisciplinary approach in the field of cerebellar research.