  We review cosmological solutions of type II superstrings and M-theory,
emphasizing the role of non-vanishing Ramond form backgrounds.
Compactifications on flat and, more generally, maximally symmetric spatial
subspaces are presented. We give a physical discussion of both inflating and
subluminally expanding cosmological solutions of such theories and explore
their singularity structure. An explicit example, in the context of the type
IIA superstring, is constructed. We then analyze compactifications of M-theory
on Ricci flat manifolds. The external part of U--duality and its relation to
cosmological solutions is studied in the low energy theory. In particular, we
investigate the behaviour of important cosmological properties, such as the
Hubble parameters and the transition time between two asymptotic regions, under
U-duality transformations. Motivated by Horava-Witten theory, we present an
explicit example of manifestly U-duality covariant M--theory cosmology in a
five-dimensional model resulting from compactification on a Calabi-Yau
three-fold.
