The second edition is mainly an expansion of the material in the first edition. The changes were made to (1) increase the clarity of the presentation, (2) extend some of the basic ideas, and (3) indicate further practical details. 1 have resisted the urgings (both from others and myself) to include more difficult codes, such as Reed-Muller, Vitcrbi, Fire, and cyclic. They seem to be more suitable for a second course, and in any case require a firmer mathematical background than 1 have assumed, if they are to be ''understood.'' I still believe that it is better, in this subject, to master the fundamentals than it is to rush through, with little real understanding, a large body of material. There are now many excellent texts devoted to algebraic coding theory.