Past to future: ROSAT to eROSITA

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian/German Spektrum-Roentgen-Gamma (SRG) mission which is current scheduled for launch in 2018. In the soft band (0.5-2 keV), the deep All-sky survey will be 30 times more sensitive than the previous ROSAT All-sky survey, while the first ever true all-sky survey will be mapped in the hard band (2-8 keV). Although its design driving science is the detection of large samples of galaxy clusters for studying the large scale structure in the Universe and test cosmological models, eROSITA will yield a sample of around 3 million active galactic nuclei. This is bound to revolutionize our view of the evolution of supermassive black holes and their impact on the process of structure formation in the Universe.The talk reports on the eROSITA scientific prospect and how the German eROSITA consortium is activated for ensuring an adequate follow-up of the sources to be discovered. The talk will also reports the work in progress in the follow-up and scietific exploitation of those AGN that ROSAT have already discovered and eROSITA will revisit.