RMS Queen Mary 2 (QM2) is a British transatlantic ocean liner. She has served as the flagship of Cunard Line since succeeding Queen Elizabeth 2 in 2004. The ship was officially named Queen Mary 2 by Queen Elizabeth II in 2004 after the first RMS Queen Mary of 1936. With the retirement of Queen Elizabeth 2 in 2008, Queen Mary 2 is the only ocean liner in service in the world. It has a regular service between Southampton, England, and New York City, United States, and an annual world cruise.

This is a timeline of the world's largest passenger ships based upon internal volume, initially measured by gross register tonnage and later by gross tonnage. This timeline reflects the largest extant passenger ship in the world at any given time. If a given ship was superseded by another, scrapped, or lost at sea, it is then succeeded. Some records for tonnage outlived the ships that set them - notably the SS Great Eastern, and RMS Queen Elizabeth. The term "largest passenger ship" has evolved over time to also include ships by length as supertankers built by the 1970s were over 400 metres (1,300 ft) long. In the modern era the term has gradually fallen out of use in favor of "largest cruise ship" as the industry has shifted to cruising rather than transatlantic ocean travel. While some of these modern cruise ships were later expanded, they did not regain their "largest" titles.