The 9th International Symposium on High Energy Spin Physics was held in Bonn, 6-15 September 1990, with the Physikalisches Institut der Universitat Bonn as the host. The symposium was preceded by a series of four workshops on • polarized electron sources and electron spin polarimeters • Siberian snakes and polarization in circular machines • polarized gas targets • polarized solid targets. 160 participants from 11 countries, among them many young physicists, came together and discussed mainly technological spin problems. The high level of participation indicates that workshops combined with the symposium are attractive not only for people who plan and prepare polarized beams and targets but also for experimentalists and theorists dealing with high energy spin physics. At these workshops many very interesting and important recent results were presented and reviewed. Thus we hope these proceedings will be valuable to many researchers in these fields. The Organizing Committee would like to thank all participants, in particular the speakers and the session chairmen, for their contributions to the workshops and for helping to create a lively and stimulating atmosphere. Special thanks go to the organizers - W. Haeberli, S. Mango, E. Reichert, E. Steffens, W. Thiel, U. Wienands - for their cooperation in preparing and running these workshops. We gratefully acknowledge the enthusiastic help of the members of our institute in preparing and running the conference and the workshops, especially Mrs. D. FaSbender, Mrs. E. Wendorf, Mrs. J. Wetzel, and Dr. U.Idschok.