This volume is a timely and comprehensive description of the many facets of DNA and RNA modification-editing processes and to some extent repair mechanisms. Each chapter offers fundamental principles as well as up to date information on recent advances in the field (up to end 2008). They ended by a short ‘conclusion and future prospect’ section and an exhaustive list of 35 to up to 257 references (in average 87). Contributors are geneticists, structural enzymologists and molecular biologists working at the forefront of this exciting, fast-moving and diverse field of researches. This book will be a major interest to PhD students and University teachers alike. It will also serve as an invaluable reference tool for new researchers in the field, as well as for specialists of RNA modification enzymes generally not well informed about what is going on in similar processes acting on DNA and vice-versa for specialists of the DNA modification-editing and repair processes usually not much acquainted with what is going on in the RNA maturation field. The book is subdivided into 41 chapters (740 pages). The common links between them are mainly the enzymatic aspects of the different modification-editing and repair machineries: structural, mechanistic, functional and evolutionary aspects. It starts with two general and historical overview of the discovery of modified nucleosides in DNA and RNA and corresponding modification-editing enzymes. Then follows eleven chapters on DNA modification and editing (mechanistic and functional aspects). Two additional chapters cover problems related to DNA/RNA repair and base editing by C-to-U deaminases, followed by three chapters on RNA editing by C-to-U and A-to-I type of deamination. Discussions about interplay between DNA and RNA modifications and the emergence of DNA are covered in two independent chapters, followed by twenty chapters on different but complementary aspects of RNA modification enzymes and their cellular implications. The last chapter concerns the description of the present state-of-the art for incorporating modified nucleosides by in vitro chemical synthesis. At the end of the book, six appendicies give useful details on modified nucleosides, modification-editing enzymes and nucleosides analogs. This information is usually difficult to obtain from current scientific literature.