THESTUDYOF“SIGNALSANDSYSTEMS” has formeda cornerstone for the development of digital signal processing and is crucial for all of the topics discussed in this Handbook. While the reader is assumed to be familiar with the basics of signals and systems, a small portion is reviewed in this chapter with an emphasis on the transition fromcontinuous time to discrete time. The reader wishing more background may find in it any of the many fine textbooks in this area, for example [1]-[6].