Formal or informal associations of human beings, usually in pursuit of some common goal
- Idaho, Libertarian Party of
- Illinois, Libertarian Party of
- Independent Institute - Aims to redefine the debate over public issues
- Independent Thought, Center for - Non-profit educational foundation based in New York City
- Indiana, Libertarian Party of
- Institut Coppet - French institute aimed at disseminating free market writings and translations
- Institute of Economic Affairs - UK's original free-market think-tank
- Instituto Liberal do Rio de Janeiro - Aims to persuade Brazilians of advantages of classical liberalism
- International Anti-Aging Conference - Holds annual conferences on healthy aging and life extension
- Iowa, Libertarian Party of