Imamia Students Organisation, an Islamic organization in Pakistan Independent system operator, a North American organization that coordinates, controls and monitors the operation of the electrical power system Internal Security Organisation, a government security agency in Uganda International Socialist Organization, United States Trotskyist organization, active from 1976 to 2019 International Socialist Organisation (Australia), Australian Trotskyist organization, active from 1971 to 2008 International Socialist Organisation (Germany), German Trotskyist organisation, established in 2016 International Socialist Organisation (New Zealand), New Zealand Trotskyist organization, founded in the early 1990s International Organization for Standardization List of International Organization for Standardization standards, a list of ISO standards Interstedelijk Studenten Overleg (Dutch National Students Association), the Netherlands Iran Scout Organization