Sleep-wake disorders frequently give rise to severe ailments and varied distresses in a great number of people in the world, disturbing their physical and mental activities and their social function. Sleep-wake disorders are now classified into a great number of cate­ gories according to their clinical features and etiological factors. Patients with sleep-wake disorders are taken care of not only by specialists for such disorders but also by general physicians and specialists of different physical and mental disorders. In the recent years, the nature of sleep and sleep-wake disorders have been intensively studied by investiga­ tors belonging to different fields of science including medicine, biology, and psychology in many countries. It is very important for the progress of research that investigators work­ ing in the related fields in different countries meet together and exchange their findings and ideas. The Japanese-German International Symposium on Sleep-Wake Disorders was held on October 9-10th, 1996 in the old, beautiful city of Erfurt (Germany). This symposium was organized by Professor Karlheinz Meier-Ewert (Schwalmstadt, Germany) and Dr. Masako Okawa (Ichikawa, Japan), with support of the German Society of Sleep Research (President at that time, Professor J. H. Peter) and of the Japanese Society of Sleep Research (President at that time, Professor Y. Hishikawa).