A navigator is the person onboard a ship or aircraft responsible for its navigation. The navigator's primary responsibility is to be aware of ship or aircraft position at all times. Responsibilities include planning the journey, advising the Captain or Aircraft Commander of estimated timing to destinations while en route, and ensuring hazards are avoided. The navigator is in charge of maintaining the aircraft or ship's nautical charts, nautical publications, and navigational equipment, and generally has responsibility for meteorological equipment and communications.

In the world's air forces, modern navigators are frequently tasked with weapon systems employment and co-pilot type duties depending on the type, model and series of aircraft. In the U.S. Air Force, the former aeronautical rating of Navigator has been renamed Combat Systems Officer, while in the U.S. Navy and U.S. Marine Corps, those officers formerly called Navigators or Naval Aviation Observers have been known as Naval Flight Officers since the mid-1960s. USAF Navigators/Combat Systems Officers and USN/USMC Naval Flight Officers must be Basic Mission Qualified in their aircraft, or fly with an Instructor Navigator or Instructor NFO to provide the necessary training for their duties.

Shipborne navigators in the U.S. Navy are normally Surface Warfare Officer qualified with the exception of Naval Aviators and Naval Flight Officers assigned to Ship's Navigator billets aboard aircraft carriers and large deck amphibious assault ships and who have been qualified at a level equal to Surface Warfare Officers. U.S. Coast Guard officers that are shipboard navigators are normally Cutter qualified at a lebel analogous to the USN officers previously mentioned. Quartermasters are the Navigator's enlisted assistants and perform most of the technical navigation dutues.

Aboard ships in the Merchant Marine and Merchant Navy, the Second Mate is generally the Navigator.

Nautical charts

detail: Nautical charts

The nature of a waterway depicted by a chart changes regularly, and a mariner navigating on an old or uncorrected chart is courting disaster. Every producer of navigational charts also provides a system to inform mariners and aviators of changes that affect the chart. In the United States, chart corrections and notifications of new editions are provided by various governmental agencies by way of Notices to Airmen (NOTAMs), Notice to Mariners, Local Notice to Mariners, Summary of Corrections, and Broadcast Notice to Mariners. Radio broadcasts give advance notice of urgent corrections.

A convenient way to keep track of corrections is with a Chart and Publication Correction Record Card system. Using this system, the navigator does not immediately update every chart in the portfolio when a new Notice to Mariners arrives, instead creating a card for every chart and noting the correction on this card. When the time comes to use the chart, he pulls the chart and chart's card, and makes the indicated corrections on the chart. This system ensures that every chart is properly corrected prior to use.