the discovery of the "splicing" of the gene transcripts, the list would include the whole molecular genetics of the lambda bacteriophage, the notions of "promotor," "repressor," and "integration," the discovery of the reverse flow of genetic information, the very existence of oncogenes, the S'-terminal "cap" struc­ ture of eukaryotic mRNAs, ... Electronmicroscopy, ultracentrifugation and tissue culture were the landmarks on the way of the young science. During the past few years, however, a major (and not so silent) revolution took place: recombinant DNA technology with all its might entered in our laboratories, and restriction mapping of cloned genomes and sequencing gels have replaced plaque counting and sucrose gradients. The new techniques have made it possible to "dissect" the entire genome of a virus at the molecular level, and studies that would have been dreamt of just in the mid-seventies became the everyday experiments of our days. With new insight into the structure of viral genomes, and a deeper understanding of the mechanisms that regulate their expression, our view of viruses was bound to change: this volume bears witness to this impressive advance.