  We consider a system made up of exictations of a neutral scalar field, \phi,
having a \lambda\phi^4 interaction term. Starting from an ensemble where the
occupation number f is large, but \lambda f is small, we develop a classical
field theory description of the evolution of the system toward equilibrium. A
Boltzmann equation naturally emerges in this description and we show by
explicit calculation that the collision term is the same as that coming from
elastic scattering. This shows the equivalence of a Boltzmann equation
description and a classical field theory description of the same system.
