VHF and UHF communications is largely possible only with stations that are in line-of-sight or slightly over the horizon.

A repeater is a radio capable of receiving on one frequency while simultaneously transmitting what it receives on another frequency. It's common to find repeaters that have advantageous placement (high up on buildings, terrain features or antenna masts), high-gain antennas and high-wattage transmitters. Some repeater systems expand their range with passive listening stations connected by point-to-point links to the transmitter; hams developed technology for the listening stations to determine which one would send the incoming signal to the main antenna for retransmission.

Modern wireless telephony technology was developed from amateur radio repeaters. Many radio systems used by law enforcement, fire/rescue and businesses use this technology.

A good repeater expands even a handheld's range "footprint" from a few square miles to hundreds or even thousands of square miles. Most VHF and UHF amateur radios are easy to program with a repeater's "offset", so that the radio is tuned to the repeater's transmit frequency but shifts to the repeater's receive frequency when transmitting.

Most amateur radio repeaters are "open," meaning that any licensed amateur can use them as long as they respect good amateur practice. "Closed" repeaters may not be used except with the explicit permission of the owner. There are some closed amateur repeaters out there, but they're few and far between. The vast majority of GMRS repeaters are closed.

Some amateur radio repeaters are linked (or can be dynamically linked by DTMF commands) to others over the Internet, allowing someone with a 5W handheld transceiver to talk to folks thousands of miles away.