The birth and the development of molecular biology and, subsequently, of genetic engineering and biotechnology cannot be separated from the advancements in our knowledge of the genetics, biochemistry and physiology of bacteria and bacter- phages. Also most of the tools employed nowadays by biotechnologists are of bacterial (or bacteriophage) origin and the playground for most of the DNA manipulations still remains within bacteria. The relative simplicity of the bacterial cell, the short gene- tion times, the well defined and inexpensive culturing conditions which characterize bacteria and the auto-catalytic process whereby a wealth of in-depth information has been accumulated throughout the years have significantly contributed to generate a large number of knowledge-based, reliable and exploitable biological systems. The subtle relationships between phages and their hosts have produced a large amount of information and allowed the identification and characterization of a number of components which play essential roles in fundamental biological p- cesses such as DNA duplication, recombination, transcription and translation. For instance, to remain within the topic of this book, two important players in the or- nization of the nucleoid, FIS and IHF, have been discovered in this way. Indeed, it is difficult to find a single fundamental biological process whose structural and functional aspects are better known than in bacteria.