The Helmholtz Zentrum Berlin (HZB) has emerged in the beginning of 2009 from the merger of BESSY and the Hahn-Meitner Institute. The new centre thus operates two large scale facilities for the investigation of structure and function of matter: the research reactor BER II, for experiments with neutrons, and the electron storage ring facility BESSY II for the production of synchrotron radiation. The HZB also operates the Metrology Light Source, a dedicated storage ring for the German National Metrology Institute PTB (Physikalisch-Technische-Bundesanstalt). The storage ring BESSY II in Adlershof is at present Germany's largest third generation synchrotron radiation source. BESSY II emits extremely brilliant photon pulses ranging from the long wave terahertz region to hard X rays. The 46 beamlines at the undulator, wiggler, and dipole sources offer users a many-faceted choice of experimental stations. The combination of brilliance and photon pulses makes BESSY II the ideal microscope for space and time, allowing resolutions down to femtoseconds and picometres. The research reactor BER II delivers neutron beams for a wide range of scientific investigations, in particular for materials sciences. Both thermal and cold neutrons are generated and used for experiments on a total of 24 measuring stations. The HZB offers highly specialised sample environments, allowing for such experiments to take place in high magnetic fields and a wide range of temperatures and pressure. The HZB aims at strengthening the complementary use of photons and neutrons for basic and applied scientific research. The centre's activities are mainly geared towards a service for an international scientific research: Every year the HZB user service arranges access to its facilities for some 2,500 external scientists (from 35 countries to date). About 100 doctoral candidates from the neighbouring universities are involved in research and training at HZB. The HZB also has extensive experience in scientific collaboration, as many beamlines and experimental stations have been build in collaboration with external research groups. There is an ongoing commitment to develop hardware and software in collaboration with other institutions for the broader scientific community. To date the HZB cooperates with more than 400 partners at German and international universities, research institutions and companies. Currently many activities focus on merging the technical and scientific support of the centre, in order to provide a more homogeneous and more effective work environment for its users. To this end the HZB also welcomes and participates in European initiatives, as for example on joint user-portals and cross-site AAA-schemes within the ESRFUP and EuroFEL work packages. With respect to its control systems, BESSY has always been a major contributor to the EPICS project and will continue to do so under the HZB banner.