Formal or informal associations of human beings, usually in pursuit of some common goal
- San Bernardino County, Libertarian Party of - California
- San Diego Libertarian Party - California
- San Francisco, Libertarian Party of - California
- Seattle Hempfest - Organizers of marijuana/hemp policy reform events in Seattle, Wash.
- Seminole County, Libertarian Party of - Florida
- Separation of School and State, Alliance for the - Aims to improve education by liberating schools from politics
- Small Government, Center for - Seeks to dismantle, reduce, and remove Big Government policies and programs
- Small Government, Committee for - Sponsored the Small Government Act in Massachusetts
- Society - Grouping of individuals interacting with each other
- South Carolina Libertarian Party
- South Dakota, Libertarian Party of
- Stateless Society, Center for a - Dedicated to building public awareness of, and support for, market anarchism
- Strana svobodných občanů (Free Citizens Party) - Czech political party advocating a lean State and individual freedom with personal responsibility
- Student Organizations - Groups organised in or across schools, colleges or universities to pursue social, political or other goals or advocate policies in educational or external institutions
- Students for Liberty - Worldwide network of pro-liberty students and student organizations
- Swiss Mises Institute - Swiss institute aiming to spread knowledge of the Austrian school of economics