IceCube, the world largest high-energy-neutrino telescope, was completed in December 2010. It provides a boost in sensitivity that will make the next 3 to 4 years extremely exciting and will hopefully lead to the first detection of extraterrestrial high-energy-neutrino sources.

Another messenger to explore the high-energy universe are gamma rays. Gamma-ray telescopes like VERITAS, MAGIC, and H.E.S.S. (all with DESY participation) have discovered more than a hundred sources of TeV gamma rays over the last years. A new-generation experiment, the Cherenkov Telescope Array CTA, will continue this success story. CTA is presently in the preparation phase with various contributions by DESY, for instance a telescope prototype and simulation studies. With more than 100 telescopes, the discovery potential for galactic and extragalactic sources will increase considerably.

In theoretical astroparticle physics we investigate particle acceleration in many sources that emit very energetic particles. These theoretical studies are necessary for the interpretation and direction of the research work of experimental physicists.

Astrophysics with high-energy neutrinos and gamma rays opens new windows to explore the universe at the highest energies. The aim is to find answers to fundamental questions as:

• the origin of cosmic rays,
• the search for dark matter and other exotic parts of the cosmic inventory and
• the study of particle physics in hitherto unexplored regions of the parameter space.