  A manifestly U-duality covariant approach to M-theory cosmology is developed
and applied to cosmologies in dimensions D=4,5. Cosmological properties such as
expansion powers and Hubble parameters turn out to be U-duality invariant in
certain asymptotic regions. U-duality transformations acting on cosmological
solutions, on the other hand, shift the transition time between two asymptotic
regions and determine the details of the transition. Moreover, in D=5, we show
that U-duality can map expanding negative and positive branch solutions into
each other.
