  This paper proposes a new semi-analytic modelling of galaxy properties in the
IR/submm wavelength range, which is explicitly set in a cosmological framework.
This type of approach has had some success in reproducing the optical
properties of galaxies. We hereafter propose a simple extension to the IR/submm
range. We estimate the IR/submm luminosities of ``luminous UV/IR galaxies'',
and we explore how much star formation could be hidden in
heavily--extinguished, ``ultraluminous IR galaxies'' by designing a family of
evolutionary scenarios which are consistent with the current status of the
``cosmic constraints'', as well as with the IRAS luminosity function and faint
counts, but with different high-z IR luminosity densities. However, these
scenarios generate a Cosmic Infrared Background whose spectrum falls within the
range of the isotropic IR component detected by Puget et al. (1996) and
revisited by Guiderdoni et al. (1997). We give predictions for the faint galaxy
counts and redshift distributions at IR and submm wavelengths. The submm range
is very sensitive to the details of the evolutionary scenarios. As a result,
the on-going and forthcoming observations with ISO and SCUBA (and later with
SIRTF, SOFIA, FIRST and PLANCK) will put strong constraints on the evolution of
galaxies at z=1 and beyond.
