A CHARGE density wave (CDW) is a periodic symmetry-lowering redistribution of charge within a material, accompanied by a rearrangement of electronic bands (such that the total electronic energy is decreased) and usually a small periodic lattice distortion(1,2). This phenomenon is most commonly observed in crystals of reduced symmetry, such as quasi-two-dimensional(3) or quasi-one-dimensional(4) materials. In principle, the reduction of symmetry associated with surfaces and interfaces might also facilitate the formation of CDWs; although there is some indirect evidence for surface charge density waves(5-12,14), none has been observed directly., Here we report the observation and characterization of a reversible, temperature-induced CDW localized at the lead-coated (111) surface of a germanium crystal. The formation of this new phase is accompanied by significant periodic valence charge redistribution, a pronounced lattice distortion and a metal-nonmetal transition, Theoretical calculations confirm that electron-phonon coupling drives the transition to the CDW, but it appears that some other factor-probably electron-electron correlations-is responsible for the ground-state stability of this phase.