Since 1972 the European Training Programme in Brain and Behaviour Research (ETP) , a sub-organization of the European Science Foundation, has been organizing a yearly Winterschool in Zuoz, Switzerland. This course with its unique blend of high-mountain air and high-level neuroscience enjoys an immense popularity. The project to organize the 1983 Winterschool on "Sleep Mechanisms", has been an outgrowth of the frequent scientific and personal contacts between the sleep research laboratories at the Universities of ZOrich and Lyon. In selecting the scientific programme we attempted not only to obtain the participation of foremost European groups engaged in the experimental study of sleep, but to emphasize new conceptual and technical approaches. We were fortunate that numerous experts in sleep research readily agreed to participate. The announcement for the course was sent out to 1600 laboratories to call for the application of junior scientists. From the 113 applications that were received from 22 different countries, 40 participants could be selected. When we finally gathered in the Hotel Castell on a beautiful winter evening, 17 European countries and Israel were represented. The week spent together led to many intense, and sometimes heated discussions which frequently continued in the bar until the early morning hours, confir­ ming that sleep researchers are accustomed to work around the clock. At the meeting the unanimous decision was taken that the contributions should be rapidly published in a separate volume to make them accessible to a wider public.