The Royal United Services Institute, commonly known as RUSI, is a British defense and security think tank. It was founded in 1831 and is based in London. RUSI conducts research and analysis on a wide range of security issues, including terrorism, cyber security, and defense policy. It also hosts conferences and events on defense and security topics. Synonyms for RUSI include the Royal Institute for Defense Studies, the Royal Defense Society, and the Royal Military Institute. All these organizations share a similar mission of promoting security, defense, and national interests in the United Kingdom and beyond.