  Optically thick accretion disks are considered to be important ingredients of
luminous AGN. The claim of their existence is well supported by observations
and recent years brought some progress in understanding of their dynamics.
However, the role of accretion disks in optical/UV/X-ray variability of AGN is
not quite clear. Most probably, in short timescales the disk reprocesses the
variable X-ray flux but at longer timescales the variations of the disk
structure lead directly to optical/UV variations as well as affect, or even
create, the X-ray variability pattern. We urgently need a considerable progress
in time-dependent disk models to close the gap between the theory and the
stream of data coming from the AGN monitoring.
