Libertarianism is

Libertarianism is the view that each man is the absolute owner of his life, to use and dispose of as he sees fit: that all man's social actions should be voluntary: and that respect for every other man's similar and equal ownership of life and, by extension, the property and fruits of that life is the ethical basis of a humane and open society. In this view, the only — repeat, only — function of law or government is to provide the sort of self-defense against violence that an individual, if he were powerful enough, would provide for himself.

Karl Hess (1969, The Death of Politics: originally published in Playboy)