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
- Indiana, Libertarian Party of
- Institut Coppet - French institute aimed at disseminating free market writings and translations
- Instituto de Estudos Empresariais - Porto Alegre, Brazil
- Instituto Ecuatoriano de Economia Politica - IEEP - Ecuador
- Instituto Liberal do Rio de Janeiro - Aims to persuade Brazilians of advantages of classical liberalism
- Instituto Libertad y Democracia - Assists developing nations in transitioning to market economies
- International Anti-Aging Conference - Holds annual conferences on healthy aging and life extension
- International Society for Individual Liberty - Dedicated to the ideals of free markets, social tolerance and individual responsibility
- Iowa, Libertarian Party of