SOI might be an acronym or abbreviation for:

* Silicon on Insulator
* Signal operating instructions
* Service Oriented Infrastructure
* Start of injection

* Southern Oscillation Index
* Sphere of influence (astrodynamics), a term in astrodynamics
* Saturn orbit insertion
* Structure of Intellect model of human intelligence originally described by J. P. Guilford

* School of Infantry
* Shadow of Infinity, a Yu-Gi-Oh! Trading Card Game set
* Sons of Iraq, auxiliary police forces that have helped bring stability to Iraq
* Severity of Illness, medical classification
* Sphere of influence, a term in politics
* Survey of India
* State of Israel
* Soi A side street in Bangkok
* The Symphony Orchestra of India
* Skating tour, Stars on Ice

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