  The basic results of optical line broadening and four-wave mixing are deduced
from first principles based on time-dependent many-body purturbation theory.
The formalism allows us to write all the results in terms of nonequilibrium
distribution functions without the need to assume a quasiequilibrium
temperature. The connection of these results to the quantum Boltzmann equation
is shown, which is also derived from first principles. Last, specific
predictions for electron-electron scattering are reviewed.
