This book owes its beginnings to the pioneering work of Claude Shannon in 1948 on reliable communication over noisy transmission channels. Shannon's central theme was that if the signaling rate of the system is less than the channel capacity， reliable communication can be achieved if one chooses proper encoding and decodingtechniques. The design of good codes and of efficient decoding methods， initiated by Hamming， Golay， and others in the late 1940s， has since occupied the energies of many researchers. Much of tlus work is highly mathematical in nature， and a thorough understanding requires an extensive background in modern algebra and probability theory. Tlus requirement has impeded many engineers and computer scientists who are interested in applying these techniques to practical systems. One of the purposes of this book is to present the essentials of this highly complex material in such a manner that it can be understood and applied with only a minimum of mathematical background.
　　Coding researchin the 1950s and 1960s was devoted primarily to developing the theory of efficient encoders and decoders. In 1970 the first author published a book entitled An Introduction to Error-Correcting Codes， which presented the fundamen-tals of the previous two decades of work covering both block and convolutional codes. The approach was to explain the material in an easily understood manner，with a minimum of mathematical rigor. Then， in 1983， the authors published the first edition of this book. The approach again stressed the fundamentals of coding.In addition， new material on many of the practical applications of coding developed during the 1970s was introduced. Other major additions included a comprehensive treatment of the error-detecting capabilities of block codes and an emphasis on soft decoding methods for convolutional codes.
　　In the 1980s and 1990s，the coding field exploded with new theoretical develop-ments， several of which have had significant practical consequences. Three of these new developments stand out in particular： the application of binary convolutional and block codes to expanded (nonbinary) modulation alphabets，the development of practical soft decoding methods for block codes， and the discovery of soft-input， soft-output iterative decoding techniques for block and convolutional codes. These new developments have revolutionized the way coding is applied to practical systems，affecting the design of high-speed data modems， digital mobile cellular telephony，satellite and space communications， and high-density data storage， to name just a few. A total of seven new chapters covering these topics have been added to this edition： two chapters on trellis- and block-coded modulation techniques， three chapters on soft decoding methods for block codes， and two chapters on turbo and low-density parity-check codes and iterative decoding.
　　Because of the significant amount of new material and the need to maintain an emphasis on coding fundamentals， it was not possible to include certain topics in this edition. For example， the new developments in algebraic geometry codes and erasure correcting codes are not covered.