International Organized Crime

International Olympic Committee

Italian Organized Crime

Input/Output Controller

Icon of Coil

Inversion of Control, a design pattern

Independent Operating Company, usually a synonym to CLEC

IBM Open Class

Iron Ore Company of Canada

International Ornithological Congress

Intergovernmental Oceanographic Commission

Indian Ocean Commission, generally COI, but according to World Bank as well IOC

Invasion of Chaos, a booster pack in the Trading Card Game Yu-Gi-Oh! which shaped an entire metagame

International Oil Company, as opposed to NOC, which stands for National Oil Company