  A new semi-analytic modelling of galaxy evolution in the IR/submm is
hereafter outlined. This type of approach successfully reproduces the optical
properties of galaxies. We illustrate a simple extension to the IR/submm
wavelength range by taking the case of the SCDM model. We design a family of
evolutionary scenarios with star formation histories reproducing the evolution
of the overall gas and luminosity densities in the universe. These scenarios
are also consistent with IRAS data and preliminary ISO counts, and we use them
to disentangle the ``Cosmic Infared Background'' detected by Puget et al.
(1996) into discrete sources. We finally give predictions for the faint galaxy
counts and redshift distributions in various submm wavelengths, which seem to
be very sensitive to the details of the evolutionary scenarios. As a
consequence, it is easy to anticipate that the current and forthcoming
instruments, such as SCUBA, FIRST and PLANCK, will strongly constrain the
evolution of high-redshift galaxies.
