A number of models are considered for the electrical properties of the moon, and the interaction of each with the solar wind is described in detail for various angles of the interplanetary magnetic field. In general, a permanent shock will form ahead of the moon if its surface conductivity is high, a temporary shock will form if it has a very large conducting core, and no shock will form if there is a thick surface layer of poor conductivity. The rate at which the void behind the moon is filled depends on the orientation of the interplanetary field and its relative strength. The field depressions observed by Colburn et al. in the moon's plasma penumbra are explained qualitatively by the expansion of the plasma there.