Cunard Line is a British-American owned shipping company based at Carnival House in Southampton, England and operated by Carnival UK. It has been a leading operator of passenger ships on the North Atlantic for over a century.

In 1839, Canadian-born Samuel Cunard was awarded the first British transatlantic steamship mail contract, and the next year formed the British and North American Royal Mail Steam-Packet Company to operate the line's four pioneer paddle steamers on the Liverpool–Halifax–Boston route. For most of the next 30 years, Cunard held the Blue Riband for the fastest Atlantic voyage. However, in the 1870s Cunard fell behind its rivals, the White Star Line and the Inman Line. To meet this competition, in 1879 the firm was reorganized as Cunard Steamship Company, Ltd to raise capital. White Star joined the American owned International Mercantile Marine Co. in 1902. The British Government provided Cunard with substantial loans and a subsidy to build two superliners needed to retain its competitive position. Mauretania held the Blue Riband from 1909 to 1929. The sinking of her sister ship Lusitania in 1915 was one of the causes of the United States' entering the First World War. In the late 1920s, Cunard faced new competition when the Germans, Italians and French built large prestige liners. Cunard was forced to suspend construction on its own new superliner because of the Great Depression. In 1934 the British Government offered Cunard loans to finish the Queen Mary and to build a second ship, the Queen Elizabeth, on the condition that Cunard merged with the then ailing White Star line to form Cunard White-Star Ltd. Cunard owned two-thirds of the new company. Cunard purchased White Star's share in 1947; the name reverted to the Cunard Line in 1950. Winston Churchill estimated that the two Queens helped to shorten the Second World War by at least a year. Upon the end of the war, Cunard regained its position as the largest Atlantic passenger line. By the mid 1950s, it operated twelve ships to the United States and Canada. After 1958, transatlantic passenger ships became increasingly unprofitable because of the introduction of jet airliners. Cunard withdrew from its year round service in 1968 to concentrate on cruising and summer transatlantic voyages for vacationers. The Queens were replaced by the Queen Elizabeth 2 (QE2), which was designed for the dual role. In 1998 Cunard was acquired by the Carnival Corporation and five years later QE2 was replaced on the Transatlantic runs by the Queen Mary 2 (QM2). The line also operates the Queen Victoria (QV) and the brand new Queen Elizabeth (QE), which entered service in October 2010.