The Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung m. b. H. (English: Berlin Electron Storage Ring Society for Synchrotron Radiation), abbreviated BESSY, is a research establishment in the Adlershof district of Berlin. Founded on 5 March 1979, it currently operates one of Germany's 3rd generation synchrotron radiation facilities, BESSY II. Originally part of the Gottfried Wilhelm Leibniz Scientific Community, BESSY now belongs to the Helmholtz-Zentrum Berlin (since 1 January 2009).
BESSY supplies synchrotron light and provides support for science and industry. There are institutional long-time users, like the Max-Planck-Society, the German Federal Institute for Materials Research and Testing (BAM) and the national metrology institute of Germany (the PTB). Furthermore, research groups from other institutes or universities can apply for utilization (so called beam time) for certain projects.