Transposons are segments of DNA that can relocate (transpose) to different positions within the genome of a single cell. In the years since their initial discovery in 1948 by Barbara McClintock, these mobile genetic elements have come to be widely recognised as ubiquitous components of genomes representing all major branches of life; furthermore, transposons have been developed into powerful tools for molecular biology, and, in particular, funcational genomes, in wide range of organisms. More recently, transposons have been developed into a technology platform for vertebrate genetics with application areas including gene therapy, transgenesis, somatic mutagenesis (cancer research), and germ line mutagenesis for gene discovery. This book presents new and important research from around the world in this field.