Identification of (high-redshift) AGN with WFXT: lessons from COSMOS and
  CDFS
  The Wide Field X-ray Telescope (WFXT) will provide tens of millions of AGN,
with more than 4x10^5 expected at z>3. Here we review the issues present in the
identification of (large) samples of faint and high-redshift X-ray sources, and
describe a statistical, powerful tool that can be applied to WFXT catalogs. The
depth of associated optical and near infrared catalogs, needed for a reliable
and as much complete as possible identification, are also discussed, along with
the combined synergies with existing or planned facilities
