RNA is recognized as the prime candidate for the primordial molecule that underpinned the emergence of life over 3.5 billion years ago, yet it is arguably the least appreciated of all biological macromolecules. Since its discovery, the understanding of the properties and roles of RNA has undergone intermittent and periodically profound transformations, which have radically altered the understanding of genetic information. To understand these transformations, this book traces the history of molecular biology and the evolving conceptual framework of the regulation of gene expression.