On the trail of quarks, supersymmetry and extra dimensions – particle physicists at DESY inquire into the very structure of our world. Using large accelerator facilities, supercomputers and leading-edge technology at the limits of the possible, they shed light on the secrets of the universe’s fundamental forces and building blocks. In pursuit of these goals, they work in national and international networks with colleagues from all over the world. After the switch-off of the HERA accelerator in Hamburg, particle physicists at DESY now contribute their knowledge at various such large-scale, international facilities, including the particle accelerators LHC and ILC, the neutrino telescope IceCube and the gamma-ray telescope CTA. Comprehensive work in theoretical particle physics complements the research programme.