Over the past two decades the "pressure and material gaps" separating ultrahigh-vacuum surface science and technical catalysis has been bridged by coupling an apparatus for the measurement of reaction kinetics at elevated pressures with an ultrahigh-vacuum system for surface analysis. Studies with this combined methodology have provided an atomic-revel understanding of various aspects of heterogeneous catalysis such as structure/activity relationships, the role of promoters and inhibitors on catalytic activity, and the nature of the metal-metal bond in mixed-metal catalysts. These investigations have demonstrated the relevance of single-crystal studies for modeling the behavior of high surface area supported catalysts as well as the power of surface analytical techniques for characterizing adsorbed reactants and intermediates.