  In this review, a number of approaches to superstring cosmology which make
use of key features which distinguish string theory from point particle
theories are discussed, with particular emphasis on emergent scenarios. One
motivation for the discussion is the realization that, in order to describe the
evolution of the very early universe, it is necessary to go beyond a
conventional effective field theory (EFT) analysis. Some of the conceptual
problems of an EFT analysis will be discussed. The review begins with a summary
of the criteria for a successful early universe scenario, emphasizing that
cosmic inflation is not the only scenario of early universe cosmology which is
consistent with current cosmological observations. Bouncing and emergent
scenarios as interesting alternatives are introduced. Some realizations of
these scenarios from superstring theory are reviewed, e.g. String Gas
Cosmology, the Pre-Big-Bang scenario, the Ekpyrotic model, Double Field Theory
cosmology and matrix model cosmology. In light of the difficulties in obtaining
cosmic inflation from string theory (at the level of EFT), and realizing that
there are promising examples of alternative early universe scenarios which are
derived from basic principles of superstring theory, one must entertain the
possibility that the cosmology emerging from string theory will not involve an
extended period of accelerated expansion.
