This book has its origin in a letter. In November of 1959, the late Prof. Dr. WERNER MEYER-EpPLER wrote to me, asking if I would contribute to a series he was planning on Communication. His book " Grundlagen und Anwendungen der Informationstheorie" was to serve as the initial volume of the series. After protracted consideration, I agreed to undertake the job provided it could be done outside my regular duties at the Bell Telephone Laboratories. Shortly afterwards, I received additional responsibilities in my research organization, and felt that I could not conveniently pursue the manuscript. Consequently, except for the preparation of a detailed outline, the writing was delayed for about a year and a half. In the interim, Professor MEYER-EpPLER suffered a fatal illness, and Professors H. WOLTER and W. D. KEIDEL assumed the editorial re sponsibilities for the book series. The main body of this material was therefore written as a leisurc time project in the years 1962 and 1963. The complete draft of the manuscript was duplicated and circulated to colleagues in three parts during 1963. Valuable comments and criticisms were obtained, revisions made, and the manuscript submitted to the publisher in March of 1964. The mechanics of printing have filled the remaining time. If the reader finds merit in the work, it will be owing in great measure to the people with whom I have had the good fortune to be associated.