Catalysis is the science that allows facilitating the chemical processes by employing a substance (catalyst) that actively participates in the reaction mechanism while not being consumed during the process. The practical totality of the most relevant chemical processes (by volume of product) up to date involves the utilization of catalysts as a crucial part of the technology. Thus, some of the most important bulk chemicals (nitric, sulfuric, and terephtalic acids) are produced via catalytic oxidation while others such as ammonia involves catalytic hydrogenation processes. Bulk polymers such as polyethylene and polypropylene and many high added-value fine chemicals produced at lower scale are generated with the key participation of a catalyst. This book intends to provide an overview of some of the most relevant industrial catalytic technologies available today. Thus, important heterogeneous catalytic processes such as Fischer-Tropsch, three-way conversion of gaseous pollutants, and preferential oxidation of CO in H2 streams have dedicated chapters in this compendium. Deactivation of catalysts, a central issue in any catalytic technology, is adequately tackled by excellent reviews from relevant authors. The upgrading of petroleum to fuels and chemicals is also covered by including chapters on hydrocracking of heavy oils and Fischer-Tropsch-derived streams. Finally, enzymes, which can be considered as natural catalysts, are described in a review chapter as essential components involved in the production of pharmaceutical, cosmetic, food, and even bulk chemicals.