As the fifth edition of Molecular Biology of the Gene goes to press, completion of the human genome sequence is no longer news. This was not something that could safely have been anticipated when the first edition appeared in 1965; even when the fourth edition came out in 1987, few if any foresaw how quickly we would move into a world where whole genomes, not just individual genes, could be visualized and compared. There has been a comparable leap in the elucidation of protein structures as well. Thus, in the last few years, the structures of the huge molecular machines that drive the basic processes discussed in this book—DNA transcription, replication, protein synthesis, and so forth—have largely been solved at the atomic level, and many details of their inner workings revealed.