Bacteria are a large group of unicellular micro-organisms. Most bacteria have a single circular chromosome that can range in size. DNA is organised into chromosomes and, in organisms other than bacteria, it is found only in the cell nucleus. Deoxyribonucleic acid(DNA)is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. Their main role is the long-term storage of information. DNA is often compared to a set of blueprints or a code, since it contains the instructions needed to construct other components of cells. This book presents current research on bacterial DNA, DNA polymerase and DNA helicases.