Left-libertarianism, also known as left-wing libertarianism, or social libertarianism, is a political philosophy and type of libertarianism that stresses both individual freedom and social equality. Left-libertarianism represents several related yet distinct approaches to political and social theory. Its classical usage refers to anti-authoritarian varieties of left-wing politics such as anarchism, especially social anarchism, communalism, and libertarian Marxism, collectively termed libertarian socialism. A portion of the left wing of the green movement, including adherents of Murray Bookchin's social ecology, are also generally considered left-libertarian.
In the United States, left-libertarianism represents the left wing of the libertarian movement, including the political positions associated with academic philosophers Hillel Steiner, Philippe Van Parijs, and Peter Vallentyne that combine self-ownership with an egalitarian approach to natural resources. Although libertarianism in the United States has become associated with classical liberalism and minarchism, with right-libertarianism being more known than left-libertarianism, political usage of the term until then was associated exclusively with anti-capitalism, libertarian socialism, and social anarchism; in most parts of the world, such an association still predominates.
Left-libertarians are skeptical of, or fully against, private ownership of natural resources, arguing in contrast to right-libertarians that neither claiming nor mixing one's labor with natural resources is enough to generate full private property rights, and maintain that natural resources should be held in an egalitarian manner, either unowned or owned collectively. Those left-libertarians who are more lenient towards private property support different property norms and theories, such as usufruct or under the condition that recompense is offered to the local or even global community, such as the Steiner–Vallentyne school.