Accretion-collision tectonics in mobile belts is one of the most important new topics in solid earth science. A special seminar on this subject, the Oji International Seminar on Accretion Tectonics, was held from the 10th to 16th September, 1981, in Tomakomai, Hokkaido, Japan. It was sponsored by the Japan Society for the Promotion of Science and the Fujihara Foundation of Science, organizers were S. Uyeda, Earthquake Research Institute, University of Tokyo, Amos Nur, Department of Geophysics, Stanford University, and M. Hashimoto, Department of Geology, National Science Museum, Tokyo. More than fifty geoscientists, thirty from Japan and twenty from abroad, met together to present findings from their recent studies and exchange ideas about accretion-collision phenomena in the circum-Pacific mobile belts. Two field days were also spent in the Horokanai area, central Hokkaido, to examine and the Horokanai ophiolite. The the Kamuikotan high-pressure metamorphic rocks latter is a fragment of ancient ocean floor crust that has been obducted onto the Kamuikotan rocks at the time of collision of the Okhotsk Micro-continent with Asia. The seminar was by no means a large congress. However, to the best of our knowledge, it was the first international conference on accretion-collision tectonics. The meeting was highly successful and we believe that it has opened an important new era in the study of plate tectonics.