A plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and circular in form. Plasmids usually occur naturally in bacteria, but are sometimes found in eukaryotic organisms. In this book, the authors present current research in the genetics, applications and health issues relating to plasmids. Topics include the development of multifunctional plasmids for diverse biotechnological applications; plasmids as indispensable components of multipartite azospirillum genomes; structural and segregational instability in plasmid biology; and conjugal plasmid transfer and phage inhibition kinetics.