A radar picket is a radar-equipped station, ship, submarine, aircraft, or vehicle used to increase the radar detection range around a nation or military (including naval) force to protect it from surprise attack, typically air attack, or from criminal activities such as smuggling. By definition a radar picket must be some distance removed from the anticipated targets to be capable of providing early warning. Often several detached radar units would be placed in a ring to encircle a target to provide increased cover in all directions; another approach is to position units to form a barrier line.

Radar picket units may also be equipped to direct friendly aircraft to intercept any possible enemy. In British terminology the radar picket function is called aircraft direction. A ship performing this function is termed a fighter direction ship. Airborne radar pickets are generally referred to as Airborne early warning and control (AEW&C) or simply airborne early warning (AEW).

In a sense radars intended to track ballistic missiles can be thought of as radar pickets, but because such systems are also used for tracking orbital satellites and space debris the preferred term for them is space domain awareness systems.