Royal United Services Institute for Defense Studies
- Country: United Kingdom
- Type: Military
- Website: www.rusi.org
- Update: 05-01
The Royal United Services Institute for Defence Studies (RUSI; abbreviated: RUSI), an independent think tank dedicated to cutting-edge defense and security research and the leading forum for national defense, was founded by the Duke of Wellington in 1831. The website serves as RUSI's main portal for scientific research, news analysis and high-profile speeches.