Discussion about third parties in the United States, as well as Independents. Any party other than the Democratic and Republican parties is considered to be a third party.
The TEA Party is not a third party, but rather a faction of the Republican Party. The Working Families Party exists largely to endorse Democrats, but is still considered to be a third party.
Third parties are severely disadvantaged by the first-past-the-post system, causing most of them to support ranked-choice voting, approval voting, or some other alternate system. They are further disadvantaged by the winner-take-all electoral college, which awards every state's votes (except in Maine and Nebraska) to the candidate with the highest share of the vote — although this system allowed for a number of segregationists to gain electoral votes in the Deep South with a mere plurality.
Third parties seem to have no hope at winning elections, with their primary goals being to spread awareness, gain ballot access, and qualify for matching funds. That being said, a small number of victories have been achieved at the local level, the most notable of which being Jesse Ventura, the Reform Party Governor of Minnesota.
The two largest third parties are the Libertarian and Green parties, which get the most attention. The Constitution Party is the third largest, but doesn't get as much attention.
The Reform, Prohibition, and Progressive (defunct) parties are historically important.
The Party for Socialism and Liberation, and the Solidarity Party are also notable.
See also:
s/Libertarianism
s/GreenParty
s/ConstitutionParty
s/Prohibition
s/SolidarityParty