Her Majesty's Yacht Britannia is the former royal yacht of the British monarchy. She was in their service from 1954 until 1997. She was the 83rd such vessel since King Charles II acceded to the throne in 1660, and is the second royal yacht to bear the name, the first being the racing cutter built for the Prince of Wales in 1893. During her 43-year career, the yacht travelled more than a million nautical miles around the world to more than 600 ports in 135 countries. Now retired from royal service, Britannia is permanently berthed at Ocean Terminal, Leith in Edinburgh, Scotland, where it is a visitor attraction with over 300,000 visits each year.

A royal yacht is a ship used by a monarch or a royal family. If the monarch is an emperor the proper term is imperial yacht. Most of them are financed by the government of the country of which the monarch is head. The royal yacht is most often crewed by personnel from the navy and used by the monarch and their family on both private and official travels.