The available data related to the mantle/planetosphere regions of both Mars and Venus are reviewed. It is shown that there are significant similarities in these regions at the two planets. These are: 1) a transition region between the magnetosheath and the ionosphere dominated by heavy, planetary ions; 2) a transition region in which the electron population is different from both the shocked solar wind and the photoelectron ones; 3) a magnetic signature near the transition boundary; and 4) the presence of low frequency electric waves within the transition region.