The 2006 Gaede-Langmuir Award recognizes work that revealed the importance of chemical bonding, reactions, and diffusion on the electrical properties of metal-semiconductor interfaces. In addition to the surface science research that first identified correlations between interface chemical and electronic properties, this article includes results using nanoscale depth-resolved techniques that extend this work in new directions. These studies provide representative examples of chemically induced electronic defects near interfaces that play a role at metal-semiconductor junctions. Chemical correlations with local electronic states suggest new ways to predict and control Schottky barriers in the nanoscale regime. (c) 2007 American Vacuum Society.