  We review recent progress in string cosmology, where string dualities are
applied so as to obtain complete cosmological evolutions, free of any essential
singularities. Two classes of models are analyzed. The first class consists of
string gas cosmologies associated to certain thermal configurations of type II
N=(4,0) models. Finite temperature is introduced along with non-trivial
"gravito-magnetic" fluxes that lift the Hagedorn instabilities of the canonical
ensemble and restore thermal T-duality symmetry. At a critical maximal
temperature additional thermal states become massless sourcing stringy
S-branes, which facilitate a bounce between the two dual, asymptotically cold
phases. Unlike previous incarnations of pre-Big Bang cosmologies, the models
remain perturbative throughout the cosmological evolution. The second class
consists of exact solutions to classical string theory that admit a Euclidean
description in terms of compact parafermionic worldsheet systems. The Euclidean
target space corresponds to a non-singular, compact T-fold, which can be used
to construct a normalizable Hartle-Hawking wavefunction for the cosmology.
