Investigating the clustering properties of AGN is important to put tight 
constraints on how the AGN are triggered and fueled, to identify the 
properties of the AGN host galaxies, and to understand how galaxies and 
AGN co-evolve. In addition the clustering properties or the bias of AGN, 
may be related to the typical mass of DM halos in which they reside and 
allow various types of AGN to be placed in a cosmological context.
In this talk I will focus on the redshift evolution of the bias factor 
of X-ray selected Type 1 and Type 2 XMM-COSMOS AGN extracted from the 
0.5-2 keV X-ray mosaic of the 2.13 deg2 XMM-COSMOS survey. The results 
show that the bias increases with redshift with constant DM halo masses 
and that Type 1 AGN reside in more massive halos compared to Type 2 AGN 
at ~2 sigma level. This result would be expected if the two classes of AGN 
correspond to different phases of the AGN evolution sequence and 
suggests that the AGN activity is a mass triggered phenomenon and that 
different AGN phases are associated with the DM halo mass, irrespective 
of redshift z. The theoretical models which assume a quasar phase 
triggered by major mergers can not reproduce the high bias factors and 
DM halo masses found for X-ray selected BL AGN. Our work extends up to z 
~ 2.2 the z ~ 1 statement that, for moderate luminosity X-ray selected 
Type 1 AGN, the contribution from major mergers is outnumbered by other 
processes, possibly secular such as tidal disruptions or disk 
instabilities.