Demography of high redshift AGN
  High redshift AGN holds the key to understand the early structure formation
and to probe the Universe during its infancy. We review the latest searches for
high-z AGN in the deepest X-ray field so far, the Chandra Deep Field South
(CDFS) 4 Msecond exposure. We do not confirm the positive detection of a signal
in the stacked Chandra images at the position of z~6 galaxies recently reported
by Treister and collaborators. We present z>3 X-ray sources number counts in
the 0.5-2 keV band obtained joining CDFS faint detections with Chandra-COSMOS
and XMM-COSMOS detections. We use these number counts to make predictions for
surveys with three mission concepts: Athena, WFXT and a Super-Chandra.
