The R.M.S. Queen Mary was a Cunard Line ocean liner that sailed the Atlantic Ocean from 1936 to 1967. The ship was named for Mary of Teck, the consort of George V of the United Kingdom.

The Queen Mary was constructed on the River Clyde in Scotland from 1930 to 1934. When it made its maiden voyage in 1936, the Queen Mary was the second largest passenger ship ever built, at a length of 1,020 feet (311 meters) and a displacement of over 81,000 tons. In comparison, the RMS Titanic was 883 feet (270 meters) long and had a displacement of over 46,000 tons. The Queen Mary and the Titanic were both steamships (R.M.S. stands for Royal Mail Steamer).

The RMS Queen Elizabeth, the largest steamship passenger ship ever built, was launched two years later in 1938. Together, the Queen Mary and the Queen Elizabeth dominated the transatlantic passenger trade for decades. The Queen Mary was retired from service in 1967 and the Queen Elizabeth in 1968. The RMS Queen Elizabeth 2 (QE2) took over the transatlantic route in 1969. And in turn, the QE2 was replaced in 2004 by a ship named after the Queen Mary, the RMS Queen Mary 2.

Since its retirement in 1967, the Queen Mary has been permanently docked at Long Beach, California on the west coast of the United States. The ship now serves as a hotel, museum, and tourist attraction.