  Inflationary cosmology has provided a predictive and phenomenologically very
successful scenario for early universe cosmology. Attempts to implement
inflation using scalar fields, however, lead to models with serious conceptual
problems. I will discuss some of the problems, explain why string theory could
provide solutions to a subset of these problems, and give a brief overview of
``string gas cosmology'', one of the approaches to merge string theory and
early universe cosmology.
