  We make predictions for the cosmological surveys to be conducted by the
future Herschel mission operating in the far-infrared. The far-infrared bands
match the peak of the CIRB, the brightest background of astrophysical origin.
Therefore, surveys in these bands will provide essential information on the
evolutionary properties of Luminous and Ultra-Luminous Infrared Galaxies (LIGs
and ULIGs), starburst and normal galaxies. Our predictions are based on a new
phenomenological model obtained from the 15-micron luminosity function of
galaxies and AGN, fitting all the ISOCAM observables (source counts and
redshift distributions) and also the recently published Spitzer source counts
in the 24-micron band. We discuss the confusion noise due to extragalactic
sources, depending strongly on the shape of the source counts and on the
telescope parameters. We derive the fraction of the CIRB expected to be
resolved by Herschel in the different wavebands and we discuss extragalactic
surveys that could be carried on by Herschel for different scientific
puropouses (i.e. ultra-deep, deep and shallow).
