Catalysis is one of the most important technologies in our modern world. We depend on it to produce materials, such as plastics, from oil; we depend on it to produce fuel to power our cars; we depend on it to remove the pollutants emitted from the engines of those cars; we even depend on it for the functioning and growth of our own bodies. It is therefore very important that we ask ourselves the question, 'what is catalysis?' and this book does exactly that, concentrating on the most important type of catalysis for industry, namely heterogeneous catalysis. The book is split into 3 sections, dealing with the fundamentals of adsorption and reaction at surfaces, the nature of heterogeneous catalysts and their synthesis, and the applications of this technology in the modern world. This book will be useful for teachers, undergraduates, and as an introductory book for graduates specialising in catalysis and surface science.