The most important forces that influence the motion of particles in a glow discharge plasma are the electrostatic force, the ion drag force, the neutral drag force, thermophoresis, and gravity. In this article we present a transport model that predicts the distribution of particles in plasma reactors in terms of the fundamental forces that act on the particles. We compare the model predictions to experimental measurements of particle distributions in a rf parallel plate plasma reactor. ©1995 American Institute of Physics.