  We review the unique cosmological implications of the XMM-LSS survey in
association with its multi-WL follow-up: (1) Large Scale Structures traced by
X-ray clusters and AGNs, optical galaxies, weak lensing as well as
Sunyaev-Zel'dovich effect; (2) location of IR star forming galaxies and IR
(obscured) AGNs within the cosmic web. The XMM/MegaCam/VIRMOS/SIRTF data base
will provide the first comprehensive study of structure formation - from
hundreds of Mpc to galaxy scale - in close connection with environmental
processes.
