thumb|VTS [[Nijmegen, monitoring the river Waal in the Netherlands]]
thumb|Sign telling mariners to contact the [[Port of London vessel traffic service as they enter the Thames Barrier control zone]]
A vessel traffic service is a marine traffic monitoring system established by harbour or port authorities, similar to air traffic control for aircraft. The International Maritime Organization defines vessel traffic service as "a service implemented by a competent authority designed to improve the safety and efficiency of vessel traffic and protect the environment. The service shall have the capability to interact with the traffic and respond to traffic situations developing in the vessel traffic service area". Typical vessel traffic service systems use radar, closed-circuit television, VHF radiotelephony and automatic identification system to keep track of vessel movements and provide navigational safety in a limited geographical area.
In the United States, vessel traffic services are established and operated by the Coast Guard Navigation Center. Some services operate as partnerships between the Coast Guard and private agencies.
Personnel
Guidelines require that the vessel traffic service authority should be provided with sufficient staff, appropriately qualified, suitably trained and capable of performing the tasks required, taking into consideration the type and level of services to be provided in conformity with the current International Maritime Organization guidelines on the subject.
International Association of Marine Aids to Navigation and Lighthouse Authorities Recommendation V-103 is the recommendation on Standards for training and certification of vessel traffic service personnel. There are four associated model courses, V103/1 to V-103/4, which are approved by the International Maritime Organization and should be used when training personnel for the vessel traffic service qualifications.
Information service
An information service is a service to ensure that essential information becomes available in time for onboard navigational decision-making.
The information service is provided by broadcasting information at fixed times and intervals or when deemed necessary by the vessel traffic service or at the request of a vessel, and may include for example reports on the position, identity and intentions of other traffic; waterway conditions; weather; hazards; or any other factors that may influence the vessel's transit.