GTS Millennium is a Celebrity Cruises ship which was built at Chantiers de l'Atlantique in St. Nazaire, France. She is the flagship of the Millennium-class cruise ships and her sister ships are Constellation, Infinity, and Summit.

When she was launched back in 2000, she was the first ship in the world to utilise a turbo-electric COGAS power plant. COGAS stands for combined gas and steam and it means the ship's green credentials were better than her predecessors. The ship will be overhauled in February 2019 with several changes taking place. For instance, the Cellar Masters will be transformed into a gastro bar and her Michael's Club will be converted into a Retreat Lounge for suite passengers.