A Remotely Operated Vehicle (ROV) is essentially a tethered underwater robot that allows the vehicle's operator to remain in a comfortable environment while the ROV works in the hazardous environment below. The total ROV system is comprised of the vehicle, which is connected to the control van and the operators on the surface by a tether or umbilical - a group of cables that carry electrical power, video and data signals back and forth between the operator and the vehicle - a handling system to control the cable dynamics, a launch system and associated power supplies. High power applications will often use hydraulics in addition to electrical cabling. In many cases, the umbilical includes additional strength members to allow recovery of heavy devices or wreckage

Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle’s capabilities. These may include sonars, magnetometers, a still camera, a manipulator or cutting arm, water samplers, and instruments that measure water clarity, light penetration and temperature.

ROVs can vary in size from small vehicles with TVs for simple observation up to complex work systems, which can have several dexterous manipulators, TV's, video cameras, tools and other equipment. The mechanism of the top hat handling system, which contains deployable neutrally buoyant cable for local excursions. Such handling techniques allow the heavy umbilical to remain vertical in the water column while the ROV maneuvers with the smaller cable, free of the surface dynamics, which in many cases, can pull the ROV from its work station.

Today, advanced technology is allowing many ROVs to shed their cable, and thus become free to roam the ocean with out such physical constraints. These emerging systems, which are battery operated, are called autonomous underwater vehicles (AUVs) and are used for ocean search and oceanographic research.