This chapter addresses the similarities between communication and radar systems. A key element in this comparison was the signal type used by either system and the associated time domain as well as frequency domain characteristics. The chapter provides an overview of elements of signals and systems that are relevant to radar systems is presented. It is assumed that the reader has sufficient and adequate background in signals and systems as well as in Fourier transform and its associated properties. In general, electrical signals can represent either current or voltage and may be classified into two main categories: energy signals and power signals. Energy signals can be deterministic or random, while power signals can be periodic or random. Signals that contain significant frequency composition at a low frequency band including DC are called lowpass (LP) signals. Advances in computer hardware and in digital technologies completely revolutionized radar systems signal and data processing techniques.