The purpose of this book is to bring to interested readers (professionals and laypersons alike) an appreciation and a basic understanding of what the genetic code is and why it has come to revolutionize thinking about living systems as a whole. The consequences of this revolution in molecular biology are so vast as to be almost incomprehensible. It seems important in a democratic society to have a citizenry well informed about the crucial issues of the day, such as genetic engineering and molecular medicine, which impact the social order and the ethos of society in such a profound way. This book discusses concisely the genetic code - what it is and how it provides the key to molecular biology. The structures of DNA (as revealed by Watson and Crick) and of the various forms of RNA are described in some detail, and it is shown how these structures are marvellously adapted to the twin problems of inheritance of traits and faithful development of individual organisms. In this latter respect, the role of proteins as the "molecules of life" is described and the central dogma of molecular biology (information flows from DNA to RNA to protein) elaborated. In addition, theories of the origin and development of the universal genetic code are reviewed briefly, and a perspective concerning the impact of molecular biology on the social ethos is presented.