High resolution electron energy loss spectroscopy (HREELS) is used to characterize the extreme surface composition and the interfaces of silane and thiol monolayers deposed on silicon and platinum crystals, respectively. Energy losses due to impact interactions are very sensitive to the molecular groups present in the extreme surface of the film. Long range dipole interactions can supply information about buried interfacial bonds. Silicon substrates were characterized before and after molecular interactions, Energy losses assigned to interfacial siloxane bonds clearly vary with previous substrate annealing. Spectra of adsorbed thiols are dominated by losses corresponding to functional groups attached to the chain-end. An energy loss at 360 cm(-1) was identified as corresponding to an interfacial S-Pt bond.