The influence of telecommunications has increased steadily since the introduc- tion oftelegraphy, radio and telephony. Now, most of us are directly dependent on one or more of its many facets for the efficient execution of our work, at home, or in our leisure. Consequently, as a subject for study it has become more and more important, finding its way into a large range of higher education courses, given at a variety oflevels. For many students, telecommunications will be presented as an area of which they should be aware. The course they follow will include the essential features and principles of communicating by electromagnetic energy, without developing them to any great depth. For others, however, the subject is of more specialized interest; they will start with an overview course and proceed to specialize in some aspects at a later time. We have written our book with both types of student in mind. We have brought together a broader range of material than is usually found in one text, and we have tried to combine an analytical approach to important concepts with a descriptive account of system design. In several places we have stressed the approximate nature of analysis, and the need to exercise engineering judgement in its application. The intention has been to avoid too much detail, so that the text will stand on its own as a general undergraduate-level introduction, and it will also provide a strong foundation for those who will eventually develop more specialized interests.