When radar systems are discussed in the literature or the remainder of this text, it is in the context of a sensor providing observations of the environment. While some of those measurements are responses from coherent waveforms of finite duration, the environment is treated as stationary with at most linear motion on the targets. Target tracking addresses the integration of measurements into a longer-term picture as illustrated in Figure 19-1. Target tracking is separated into two parts: track filtering and measurement-to-track data association.