Imagine that a young physicist would approach a granting agen­ cy and propose to contribute to heterogeneous catalysis by studying the heat conductivity of gases in contact with a hot filament. How would he be received now? How would he have been treated sixty years ago ? Yet, more than sixty years ago, Irving Langmuir, through his study of heat transfer from a tungsten filament, uncovered most of the fundamental ideas which are used to-day by the scientific com­ munity in pure and applied heterogeneous catalysis. Through his work with what were for the first time "clean" metal surfaces, Langmuir formulated during a period of a little over ten years un­ til the early thirties, the concepts of chemisorption, monolayer, adsorption sites, adsorption isotherm, sticking probability, cata­ lytic mechanisms by way of the interaction between chemisorbed spe­ cies, behavior of non-uniform surfaces and repulsion between adsor­ bed dipoles. It is fair to say that many of these ideas constituting the first revolution in surface chemistry have since been refined through thousands of investigations. Countless papers have been pu­ blished on the subject of the Langmuir adsorption isotherm, the Langmuir catalytic kinetics and the Langmuir site-exclusion adsorp­ tion kinetics. The refinements have been significant. ThE original concepts in their primitive or amended form are used everyday by catalytic chemists and chemical engineers allover the world in their treatment of experimental data, design of reactors or inven­ tion of new processes.