IO
- io – (s) Ido language (ISO 639-1 code)
- IO – (s) British Indian Ocean Territory (ISO 3166 digram; FIPS 10-4 territory code)
- IOC – (i) Initial Operational Capability – Intergovernmental Oceanic Commission – International Olympic Committee – International Ornithological Congress
- IOM – (i) Iowa, Ohio, Michigan (soybean origin) – Institute of Medicine – International Organisation for Migration – Isle of Man
- IONA – (i) Islands of the North Atlantic (alternate name for Great Britain, Ireland, the Isle of Man, and related islands)
- IOT – (s) British Indian Ocean Territory (ISO 3166 trigram)
- IOT&E – (i) Initial Operational Test and Evaluation
- IOU – (p) "I Owe You" (Promissory note)
Read more about this topic: List Of Acronyms And Initialisms: I