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����It is gratifying that this textbook is still sufficiently popular to warrant a third edition. I have used the opportunity to improve and enlarge the book.����When the second edition was prepared�� only two pages on algebraic geometry codes were added. These have now been removed and replaced by a relatively long chapter on this subject. Although it is still only an introduction�� the chapter requires more mathematical background of the reader than the remainder of this book.����One of the very interesting recent developments concerns binary codes defined by using codes over the alphabet 24. There is so much interest in this area that a chapter on the essentials was added. Knowledge of this chapter will allow the reader to study recent literature on 24-codes.����Furthermore�� some material has been added that appeared in my Springer Lecture Notes 201�� but was not included in earlier editions of this book�� e. g. Generalized Reed-Solomon Codes and Generalized Reed-Muller Codes. In Chapter 2�� a section on "Coding Gain"��the engineer's justification for using error-correcting codes��was added.