We present a method for interpreting scanning tunneling microscope (STM) images of surfaces, and apply this method to the Si(111)2 × 1 surface. We demonstrate how the STM does not directly image the atoms on a surface. Rather, the images reveal the spatial distribution of those electronic states lying near the Fermi-level. For semiconductors, a given wave-function is often preferentially localized on specific atoms or bonds. A lowest order interpretation of the images thus requires a description of the surface wave-functions, and a simple method for qualitatively constructing the wave-functions is illustrated here. Using this method, we demonstrate that STM images of the Si(111)2 × 1 surface are consistent with the Π-bonded chain model for this surface, and inconsistent with the Π-bonded molecular model and the buckled model. © IOP Publishing Ltd.