This chapter includes discussions on the average radar cross section (RCS) of targets and clutter, their fluctuation properties, and the detection of targets in the presence of noise and clutter. It specifically addresses, when possible, the causes for variation in the RCS of targets and clutter, and the statistical principles used in radar echo analysis. Example RCS values applicable to AEW are given for targets and clutter. Statistical target and clutter models that have proved useful for radar system analyses are also discussed. Finally, basic background material and sample problems are included on the detection of targets in the presence of noise and clutter.