String cosmology

I discuss some recent developments in string cosmology. The first is based on the low energy string action in a pre big bang cosmology in which the dynamics of the massless fields (dilaton, graviton, moduli and axion) play a pivotal role, leading to a period of inflation and the possibility of a spectrum of near scale invariant density perturbations. The second is a method to dynamically stabilise the dilaton through the presence of non-perturbative gaugino condensates in a supergravity action. It relies on the presence of exponential potentials which lead to cosmological scaling solutions.