The IMO number of the International Maritime Organization is a generic term covering two distinct meanings. The IMO ship identification number is a unique ship identifier; the IMO company and registered owner identification number is used to identify uniquely each company and/or registered owner managing ships of at least 100 gross tons (gt). The schemes are managed in parallel, but IMO company/owner numbers may also be obtained by managers of vessels not having IMO ship numbers. IMO numbers were introduced to improve maritime safety and reduce fraud and pollution, under the International Convention for the Safety of Life at Sea (SOLAS).

Atlantic Star was a cruise ship built in 1984. She sailed for Sitmar Cruises, Princess Cruises, P&O Cruises Australia, and Pullmantur Cruises. Under ownership of Royal Caribbean Cruises Ltd., the ship had been laid up since 2010 before being handed over to STX France in 2013 as a partial payment for the construction of what is now, Harmony of the Seas. She was later sold to a shipbreaker in Aliağa, Turkey, renamed Antic, and scrapped on 14 April 2013.