Restriction enzymes cleave DNA at specific recognition sites and have many uses in molecular biology, genetics, and biotechnology. More than 4000 restriction enzymes are known today, of which more than 621 are commercially available, justifying their description by Nobel Prize winner Richard Roberts as "the workhorses of molecular biology." This book by Wil Loenen is the first full-length history of these invaluable tools, from their recognition in the 1950s to the flowering of their development in the 1970s and 1980s to their ubiquitous availability today. Loenen has worked with restriction enzymes throughout her career as a research scientist, during which she came to know many of the leaders in this field personally and professionally. She is the author of several authoritative and widely appreciated reviews of the enzymes' biology. Her book was written with the close assistance of several of the field's pioneers, including Rich Roberts, Stuart Linn, Tom Bickle, Steve Halford, and the late Joe Bertani. The seed for the book was sown at a retirement party for Noreen Murray, to whom the book is dedicated, and its roots lie in a remarkable 2013 conference at Cold Spring Harbor Laboratory that celebrated the people and events that were vital to the field's development. Funding for the book was made possible by the Genentech Center for the History of Molecular Biology and Biotechnology at Cold Spring Harbor Laboratory.