Book excerpt: This book opens with an essay on the historical perspective of the study of plasmids, reviewing important events and discoveries that have propelled the field forward. The remaining chapters are divided into six sections, detailing basic biological processes such as replication and inheritance functions, specific plasmid systems, plasmid evolution, and use of plasmids as genetic tools. Chapters include use of genomic approaches for the study of plasmid biology, and a review of plasmids from bacteria, archaea, and eukaryotes is presented. In-depth treatment is given to diversity of plasmid systems in the natural environment, and the development of plasmid use in the laboratory is also covered.