We have recently simulated the phases of monolayer films of 3He adsorbed on graphite using the Feynman path-integral Monte Carlo method, realistic potential functions for the substrate-adsorbate and adsorbate-adsorbate interactions, and a three-dimensional geometry. We found the fluid, commensurate solid, incommensurate solid, and reentrant fluid phases to be in agreement with the experimental phase diagram. The microscopic structure of the reentrant fluid was observed to be a striped domain-wall liquid and is consistent with a recent experimental interpretation and theoretical model. In this paper, we describe our earlier findings and expand the simulation study of the reentrant fluid phase. Also the consequences to the structure and energetics of helium films adsorbed on an unmodulated graphite substrate are reported. © 1988 American Chemical Society.