  New techniques for evaluating the closed time path action for non-equilibrium
quantum fields are presented. A derivative expansion is performed using a
proper time kernel. Applications relevant to the scalar field theory of warm
inflation are discussed and dissipation terms resummed. The effective action of
the electromagnetic field is also considered. In this case the leading term can
be related to the conductivity of a plasma and has a simple interpretation in
terms of the classical Drude theory of conductivity.
