All we have of freedom, all we use or know—
This our fathers bought for us long and long ago.
Ancient Right unnoticed as the breath we draw—
Leave to live by no man's leave, underneath the Law.
Lance and torch and tumult, steel and grey-goose wing
Wrenched it, inch and ell and all, slowly from the King.
Till our fathers 'stablished, after bloody years,
How our King is one with us, first among his peers.
So they bought us freedom—not at little cost
Wherefore must we watch the King, lest our gain be lost,
(from) The Old Issue Rudyard Kipling
Perhaps less of a form of government than a political principle to be applied to all forms of government as the polar opposite of Authoritarianism. Libertarianism instinctively pulls towards minarchism and the night watchman state - and quite possibly autarchy, anarchy or theocracy depending on the predelictions of the population that it serves - but it has the primary principle that government, whatever its form, should not place any restriction on an individual's freedom of action that is not strictly necessary.
Necessity is generally judged on the basis of preventing harm to others1 (given that harming someone is fairly certain to reduce their freedom) - a common libertarian maxim would be that "your right to swing your fist ends where it connects with my nose".
Note that libertarian liberty tends to be strongly based on the Anglo-Saxon model of freedoms rather than the wider European model of entitlements: For example, in the matter of free speech it's not that "You" have a right to express an opinion but rather that "I" have no business stopping you unless it would cause me unjust harm. That's a fairly simple model, but the principle is as expressed.
As with authoritarianism, libertarianism is a sliding scale and differing adherents are prepared to accept differing degrees of restriction.
Game and Story Use
- May be a little unsettling for players from the developed world to find that most things that they (and therefore their PCs) would expect "the government" to do - or object to - are completely ignored in the state they are visiting.
- Likewise, if the PCs want to deal with the local government, they might not be prepared to have to wait for or arrange a town meeting and deal with the questions of nosy members of John Bull Public.
- The limits of the state in a libertarian community might not be entirely clear to outsiders - and there may be nasty surprises waiting for people that step over the line.
- A likely conflict in settings is Libertarianism as the ideology of the Frontier or other sparsely populated areas where it is easier to settle everything with mutually agreed contracts, while more government-centered ideologies will likely hold in very densely populated regions.