The book "Extracellular Nucleic Acids" offers a comprehensive examination of the role of extracellular nucleic acids in biology and medical sciences. In recent years, it has become evident that these nucleic acids not only serve as genetic elements in microbial evolution but also take on structural functions in bacterial communities, such as biofilms. Furthermore, circulating DNA and RNA have been discovered in human blood, which could serve as non-invasive markers for the diagnosis of various diseases. The book addresses the latest developments in this emerging research field and provides valuable insights into the fundamental biology, ecology, and medical applications of extracellular nucleic acids.