A studio-transmitter link sends a radio station's or television station's audio and video from the broadcast studio to a transmitter in another location.

This is often necessary because the best locations for an antenna are on top of a mountain, where a much shorter tower is required, but where a studio is completely impractical. Even in flat regions, the center of the station's allowed coverage area may not be near the studio location, so the antenna must be placed several miles or kilometres away.

Depending on the locations that must be connected, a station may choose either a point to point (PTP) link on another special radio frequency, or a newer all-digital wired link via a dedicated T1 or E1 line. Radio links can also be digital, or the older analog type, or a hybrid of the two. Even on older all-analog systems, multiple audio and data channels can be sent using subcarriers.

Stations that employ an STL usually also have a transmitter-studio link (TSL) to return telemetry information. Both the STL and TSL are considered broadcast auxiliary services (BAS).