The International Maritime Organization (IMO) number is a unique identifier for ships, registered ship owners and management companies. IMO numbers were introduced to improve maritime safety and security and to reduce maritime fraud. They consist of the three letters "IMO" followed by unique seven-digit numbers, assigned under the International Convention for the Safety of Life at Sea (SOLAS).
The IMO number scheme has been mandatory for all ships since 1 January 1996. The number identifies a ship and does not change when the ship's owner, country of registry or name changes. The ship's certificates must also bear the IMO number. Since 1 July 2004, passenger ships are also required to carry the marking on a horizontal surface visible from the air.