Sea of Thieves is a 2018 action-adventure game developed by Rare and published by Microsoft Studios. The player assumes the role of a pirate who completes voyages from different trading companies. The multiplayer game sees players explore an open world via a pirate ship from a first-person perspective. Groups of players encounter each other regularly during their adventures, sometimes forming alliances, and sometimes going head-to-head.

Sea of Thieves was conceived in 2014. Rare was inspired by players of PC games such as Eve Online (2003), DayZ (2018), and Rust (2018) who used the game tools to create their own stories. Rare explored different settings, such as vampires and dinosaurs, before settling on a pirate theme inspired by the Pirates of the Caribbean films and The Goonies (1985). The game features a progression system that only unlocks cosmetic items as the development team wanted to encourage both casual and experienced players to play together. Rare departed from its reputation for secrecy during Sea of Thieves's development, inviting fans to test early builds.

Sea of Thieves was released in March 2018 for Windows and Xbox One; it was one of the earliest first-party games released for Xbox Game Pass subscribers. It received mixed reviews; critics praised the ship combat, multiplayer, visuals, and physics, but criticized the progression, gameplay, and lack of content. Rare envisioned Sea of Thieves as a "game as a service" and has released numerous content updates after the initial release, which improved its reception. Sea of Thieves was a commercial success and became Microsoft's most successful original intellectual property of the eighth generation, attracting more than 40 million players by April 2024. A native Xbox Series X/S version of the game was released on March 13, 2024,[1] and the game was released for the PlayStation 5 on April 30, 2024, making it Rare's first game to be released on a PlayStation console.[2]