The contribution of bacteriophages to the development of modern biology cannot be overestimated yet, sixty years after their discovery, they are as remote and mysterious to many scientists as they are to most laymen. This book endeavours to remedy the situation: an attempt has been made to provide, in readily comprehensible form, a nucleus of information essential to anyone embarking on the study of bacteriophages or using them in their work for the first time. It shows the range of bacteriophage structure and behaviour; it illustrates the role of bacteriophage in molecular biology; it surveys the current state of the art; it presents the medical and industrial aspects. Some simple experimental procedures are given in sufficient detail for the beginner to attempt them successfully. Other, more sophisticated pro- cedures are presented so as to impart a feeling of intimate reality without dazzling the reader with technical complexity. I hope that young readers will forgive me for assuming that they have some knowledge of bacteria, nucleic acids, antibodies and isotopes. Likewise I would ask mature workers to excuse the omission of cherished specialities. To have included all these, valuable though they are, might have put this book beyond the re ach of the phage-novices for whom it is intended. Specific references, save a few of particular interest, have been omitted. Other books on bacteriophage v vi BACTERIOPHAGES provide them in abundance.