  These lectures present a brief review of inflationary cosmology, provide an
overview of the theory of cosmological perturbations, and then focus on the
conceptual problems of the current paradigm of early universe cosmology, thus
motivating an exploration of the potential of string theory to provide a new
paradigm. Specifically, the string gas cosmology model is introduced, and a
resulting mechanism for structure formation which does not require a period of
cosmological inflation is discussed.
