This text has its origins in our initial thought several years ago of revising and updating our first text, Digital Signal Processing, which was published in 1975. The vitality of that book attests to the tremendous interest in and influence of signal processing, and it is clear that the field continues to grow in importance as the available technologies for implementing signal processing continue to develop. Shortly after beginning the revision, we realized that it would be more appropriate to develop a new textbook strongly based on our first one and at the same time continue to have the original text also available.