  Some of the phenomenological implications of string cosmological models are
reviewed, with particular attention to the spectra of the tensor, scalar and
vector modes of the geometry. A class of self-dual string cosmological models
is presented. These solutions provide an effective description of cold bounces,
where a phase of accelerated contraction smoothly evolves into an epoch of
decelerated Friedmann--Robertson--Walker expansion dominated by the dilaton.
Some of the general problems of the scenario (continuity of the perturbations,
reheating, dilaton stabilization,...) can be successfully discussed in this
framework.
