• RSI GmbH, a german company developing 3D - Scanners and 3D - Software
• RADARSAT International, a subsidiary of MacDonald Dettwiler and Associates
• Radio Slovenia International, international service of Slovenian state radio on shortwave and via satellite
• Radio Singapore International, a news agency in Singapore
• Radiotelevisione Svizzera di lingua Italiana, a Swiss radio broadcaster
• Rapid sequence induction, a form of anesthesia
• Red Sector Incorporated, a demogroup
• Regional Systems Integrator, a small business partner of a larger company that implements software solutions at local markets.
• Relative strength index, a securities market indicator
• Religious Science International, a group of Religious Science churches
• Italian Social Republic, Repubblica Sociale Italiana
• Repetitive strain injury, a disorder affecting muscles, tendons and nerves from repetitive movements
• Required supplementary information, evaluations of governmental accounting
• Research Science Institute, a summer research program held at MIT for rising high school seniors
• Residual self image, the self-projected image of oneself in psychology and The Matrix
• Resource Software International Ltd., a communication management call accounting software company
• Revenue and Social Insurance number, in the Republic of Ireland
• Review of Scientific Instruments, title of a scientific journal
• R-value Système International, a measure of thermal resistance in SI units, see R-value (insulation)
• Right Scale of Integration or Reasonable Scale of Integration as opposed to Large-Scale Integration

Rsi may refer to:

• Rishi, a Hindu saint or sage