Symphony of the Seas is an Oasis-class cruise ship owned and operated by Royal Caribbean International. She was built in 2018 in the Chantiers de l'Atlantique shipyard in Saint-Nazaire, France, the fourth in Royal Caribbean's Oasis class of cruise ships. At 228,081 GT, she was the largest cruise ship in the world by gross tonnage when built, surpassing her sister ship Harmony of the Seas, also owned by Royal Caribbean International, and surpassed by her sister ship Wonder of the Seas in 2022.

The Oasis class is a class of 7 Royal Caribbean International cruise ships. The first two ships in the class, Oasis of the Seas and Allure of the Seas, were delivered respectively in 2009 and 2010 by STX Europe Turku Shipyard, Finland. A third Oasis-class vessel, Harmony of the Seas, was delivered in 2016 built by STX France. A fourth vessel, Symphony of the Seas, was completed in March 2018. As of March 2022, the fifth Oasis-class ship, Wonder of the Seas, was the largest cruise ship in the world. A sixth ship, Utopia of the Seas, is currently being built for entry into service in July 2024 with a seventh to follow in 2028.