Cataclysmic variables (CVs) are the most numerous compact binaries in the X-ray sky. Yet their space density and luminosity function, hence their contribution to the total energy output of the Milky Way at high energies is virtually unknown. This situation will be fundamentally changed with eROSITA. Since all types of CVs are X-ray emitters, large volume-limited samples will be constructed for the first time. Based on these we will test current population synthesis models which predict abundant low-luminosity objects.

In the first funding period of eRO-STEP (2021-2024), we have studied individual CVs and small samples of known and newly discovered CVs and candidates. In the second funding period (2024-2027), emphasis will be put on establishing and analyzing complete samples of different classes of CVs using large volume-limited samples based on the eROSITA all-sky survey. We will test current population synthesis models and quantify the effect of magnetism on CV evolution. Furthermore, the contribution of white-dwarf accretors to the Galactic Ridge X-ray Emission above 2 keV will be determined.