The emergence of fibre optics as a commercially viable technology oc­ curred barely ten years ago; in this time it has become an established field with a variety of applications. This book has been written in an attempt to review the entire field with an emphasis on the practical applications of the technology. This approach has been adopted since it was felt that there was a need for a work which could be referred to by non -specialists in the field who were interested in, or who wished to make use of, fibre optics. With this readership in mind, the theory has been presented in as simple a manner as possible and emphasis has been placed on the description of typical applications and the manufacturing techniques of the technology. It is hoped that this mode of presentation will en­ able the reader to form an appreciation of both its advantages and its limitations.