The extended ROentgen Survey with an Imaging Telescope Array: eROSITA

eROSITA is the principal instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is currently scheduled for launch in March 2016. A deep survey of the entire X-ray sky will done by eROSITA.  In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters to redshifts z > 1 in order to study the large scale structure in the Universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGN, including obscured objects, revolutionizing our view of the evolution of  supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars and diffuse emission within the Galaxy.