  The use of a nearby metallic ground-plane to limit the range of the Coulomb
interactions between carriers is a useful approach in studying the physics of
two-dimensional (2D) systems. This approach has been used to study Wigner
crystallization of electrons on the surface of liquid helium, and most
recently, the insulating and metallic states of semiconductor-based
two-dimensional systems. In this paper, we perform calculations of the
screening effect of one 2D system on another and show that a 2D system is at
least as effective as a metal in screening Coulomb interactions. We also show
that the recent observation of the reduced effect of the ground-plane when the
2D system is in the metallic regime is due to intralayer screening.
