  We consider the extension of static dimensional reduction to real-time. For a
scalar field theory it is shown that in the high-temperature limit this leads
to an effective classical theory. Quantum corrections to the leading classical
behavior are determined by an effective action which can be calculated
perturbatively in the background of the classical fields. Feynman rules for
(\lambda\phi^4)-theory are given and the extension to SU($N$) gauge theories is
outlined.
