IOI

IOI may refer to:

• Idiopathic orbital inflammatory disease
• International Olympiad in Informatics
• Interonset interval
• Indication of interest, used in financial trading
• Interest on Investment, a synonym for Return on Investment (ROI)
• IO Interactive, a Danish video game developer
• International Ombudsman Institute
• IOI Group, a Malaysian conglomerate
• I.O.I, a South Korean girl group formed from the television show Produce 101
• Innovative Online Industries (IOI), the fictional corporation that employs most of the antagonists of the 2011 novel Ready Player One and its 2018 film adaptation