This chapter addresses the basic issues of tracking airborne targets (aircraft, missiles, and so on) with a radar operating in a track-while-scan mode. Although multitarget tracking radars are of primary interest, the issues associated with tracking a single target will be addressed first. These issues are addressed first because most multitarget track algorithms act as 'executives' that pass information to subordinate singletarget track algorithms. Finally, the multiple-target tracking problem and associated algorithms will be presented.