Wide area X-ray surveys are essential for the census of the rare and bright objects, currently barely rappresented in our evolutionary models of AGN.
However, without the support of homogeneus ancillary data at the right wavelength and of sufficient depth, very little can be done for the identification (and consequent classification and redshift determination) of the sources responsible of the X-ray emission.
In this talk, I will review our work on the identification and characterization of the counterparts to the all-sky X-ray eROSITA and XMMSlew2 surveys. For the latter, I will present also the results of the associations in the Galactic Plane.
I will then conclude presenting our plans for the identification of the X-ray sources that eROSITA will detect.