Catalysis has made major contributions to many areas of chemical industry. Before embarking upon detailed considerations of catalytic science and technology, it is very helpful to look first at the nature of industrial catalysis, and how it has evolved and grown to meet demands imposed by changing industrial needs. Dr. H. Reinemann is uniquely qualified to place industrial catalysis in a historical perspective: in his distinguished industrial career he has been closely involved with many of the major innovations in industrial catalysis. Before a catalytic process is commercialized, the supporting research and development work is carried out in chemical reactors. It is obviously imperative that the behaviour of such reactor systems should be tho­ roughly understood by those who use them, and by those who may have to interpret their results, yet all too often this basic need is not met. Professor J. C. R. Turner provides a Straightforward yet thorough account of catalytic reactor theory which should make it impossi­ ble for any catalytic practitioner to plead ignorance. The catalytic hydrogenation of dinitrogen to ammonia is one of the world's great industrial processes and the catalytic activation of molecular dinitrogen is a key step in that process. The chapter by Professors A. Ozaki and K. Aika deals with the chemistry of dinitrogen activation at the catalyst surface, and shows how this relates to the synthesis of ammonia. The chapter also deals with the activation of dinitrogen by molecular complexes in homogeneaus systems.