RSI
- Italian Social Republic
- RADARSAT International
- RSI Corporation
- RSI register
- RSI-value
- Radio Singapore International
- Radio Slovenia International
- Radiotelevisione svizzera di lingua italiana
- Rapid sequence induction
- Recursive self-improvement
- Red Sea International Airport
- Red Sport International
- Reference Software International
- Regional snowfall index
- Relational Semantics, Inc.
- Relative strength index
- Religious Science International
- Repetitive strain injury
- Research Science Institute
- Residual self image
- Revenue and Social Insurance number
- Review of Scientific Instruments
- The Real
- Ṛṣi