Formal or informal associations of human beings, usually in pursuit of some common goal
- Palm Beach County, Libertarian Party of - Florida
- Pasco County, Libertarian Party of - Florida
- Pennsylvania, Libertarian Party of
- Pioneer Valley Libertarian Association - Massachusetts
- Pittsburgh, Libertarian Party of - Pennsylvania
- Policy Institutes - Organisations that conduct research on social, economic, political or other issues, publishing their findings to influence government policies
- Political Economy Research Center - Brings market principles to resolving environmental problems
- Political Parties - Groups of individuals that organise to gain control of governments at a national or other level, usually by election of candidates for government offices
- Prodos Institute, Inc., The - Dedicated to the advancement of global freedom, invention and prosperity