An early-warning radar is any radar system used primarily for the long-range detection of its targets, i.e., allowing defences to be alerted as early as possible before the intruder reaches its target, giving the air defences the maximum time in which to operate. This contrasts with systems used primarily for tracking or gun laying, which tend to offer shorter ranges but offer much higher accuracy.

Early Warning Radars tend to share a number of design features that improve their performance in the role. For instance, Early Warning Radar typically operates at lower frequencies, and thus longer wavelengths, than other types. Early Warning Radars often use much lower pulse repetition frequency to maximize their range, at the cost of signal strength, and offset this with long pulse widths, which increases the signal at the cost of lowering range resolution.