  The 2PI effective action formalism for quantum fields out of equilibrium is
set up in an expanding (Friedmann-Robertson-Walker) background. We write down
and solve the evolution equations for a phi^4 model at NLO in a coupling
expansion. We comment on issues of renormalization, lattice discretization and
the range of applicability of the approach. A number of example calculations
are presented, including thermalization and (p)reheating. Generalizations to
more complicated systems and applications are discussed.
