DESY is charged to work on a roadmap for photon science in Germany. This includes an upgrade of PETRA III into a low-emittance storage ring (horizontal emittance well below 50 pmrad) in about 10 years from now that would make undulator radiation at about 1Angström nearly diffraction limited. In preparation the workshop "Science at PETRA IV" is to explore the scientific opportunities of such a source. The workshop will be held on March 23-24, 2015 at DESY to discuss the scientific opportunities provided by such a source. We are very much looking forward to welcoming you on this occasion.