RMS Queen Mary 2 is a transatlantic ocean liner. She was the first major ocean liner built since Queen Elizabeth 2 in 1969, the vessel she succeeded as flagship of the Cunard Line. The ship was named by Queen Elizabeth II in 2004 after the first RMS Queen Mary, completed in 1936. Queen Mary was in turn named after Mary of Teck, consort of King George V. With the retirement of Queen Elizabeth 2 from active duty in 2008, Queen Mary 2 is currently the only transatlantic ocean liner in operation as a liner, although the ship is often used for cruising, including an annual world cruise.

At the time of her construction in 2003 by Chantiers de l'Atlantique, 
Queen Mary 2 was the longest, widest and tallest passenger ship ever built, and with her gross tonnage (GT) of 148,528 tons, was also the largest. She no longer holds this distinction after the construction ofRoyal Caribbean International's 154,407 GT Freedom of the Seas in April 2006, which was in turn superseded by the same company's 225,282 GT Oasis of the Seas in October 2009. However, Queen Mary 2 remains the largest ocean liner (as opposed to cruise ship) ever built.

Queen Mary 2 was intended primarily to cross the Atlantic Ocean, and was therefore designed differently from many other passenger ships. The ship's final cost was approximately $300,000 US per berth, nearly double that of many contemporary cruise ships. This was due to the size of the ship, the high quality of materials, and that, having been designed as an ocean liner, she required 40% more steel than a standard cruise ship. She has a maximum speed of 29.62 knots (54.86 km/h; 34.09 mph) and a cruising speed of 26 knots (48 km/h; 30 mph), much faster than contemporary cruise ships, such as Oasis of the Seas, which has a cruising speed of 22.6 knots (41.9 km/h; 26.0 mph). Instead of the diesel-electric configuration found on many ships, Queen Mary 2 uses a CODAG configuration in order to achieve her maximum speed. This uses additional gas turbines to augment the power given by the diesel generators onboard, and allow the ship to reach a higher maximum speed.

Queen Mary 2's facilities include fifteen restaurants and bars, five swimming pools, a casino, a ballroom, a theatre, and the first planetariumat sea. There are also kennels onboard, as well as a nursery. Queen Mary 2 is one of the few ships afloat today to have remnants of a class system onboard, most prominently seen in her dining options.