SOI might be an acronym or abbreviation for:
- Technology
- Silicon on Insulator
- Signal operating instructions
- Service-oriented infrastructure
- Start of injection
- Science
- Southern Oscillation Index
- Sphere of influence (astrodynamics), a term in astrodynamics
- Misc
- Sociosexual Orientation Inventory (SOI)
- School of Infantry
- Shadow of Infinity, a Yu-Gi-Oh! Trading Card Game set
- Sons of Iraq, auxiliary police forces in Iraq
- Severity of Illness, medical classification
- Sphere of influence, a term in politics
- Survey of India
- Sons of Intellect, a hip-hop group
- State of Israel
- Soi, a side street in Thailand
- The Symphony Orchestra of India
- Skating tour, Stars on Ice