Left-libertarianism, also known as left-wing 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.

While right-libertarianism is widely seen as synonymous with libertarianism in the United States, left-libertarianism is the predominant form of libertarianism in Europe. In the United States, left-libertarianism is the term used for the left wing of the American 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 libertarianism until then was associated exclusively with anti-capitalism, libertarian socialism, and social anarchism; in most parts of the world, such an association still predominates.

While all libertarians begin with a conception of personal autonomy from which they argue in favor of civil liberties and a reduction or elimination of the state, left-libertarianism encompasses those libertarian beliefs that claim the Earth's natural resources belong to everyone in an egalitarian manner, either unowned or owned collectively. Like other forms of libertarianism, left-libertarian views on the state usually range from minarchism, which argues for a decentralised and limited government, to anarchism, which advocates for the state to be abolished entirely.

Libertarianism is a philosophy that advocates for freedom, whether political, economical or metaphysical. Although older political movements have been identified as libertarian (for example, Marxist historian E.P. Thompson argued in 1979 that "the English left-libertarian tradition can be traced back to the Levellers, Diggers and the Chartists"), the political definition of the term "libertarian" (from the French: libertaire) was coined by the French anarchist communist Joseph Déjacque in 1857, whereafter libertarianism became synonymous with anarchism. The term was widely used by anarchists until the 1970s, when libertarianism first started to be associated with a radical free market philosophy, particularly in the United States.

The oldest, traditional, definition of "left-libertarianism" used it synonymously with social anarchism. Seeking to distinguish themselves from the new generation of free-market libertarians, social anarchists began referring to themselves as "left-libertarians", while the new adoptees of the term became known as "right-libertarians". This usage is also applied to libertarian socialists such as William Morris or Fenner Brockway and libertarian Marxists such as Cornelius Castoriadis.

At the same time as social anarchists began using the term to distinguish themselves from free-market libertarians, some of the advocates of free market economics that were associated with the New Left, including Roy Childs and Samuel Konkin, also began referring to themselves as "left-libertarians" in order to highlight themselves as the left-wing of the new free-market libertarian movement. As anti-capitalist advocates of free-market economics, they used the term "left-libertarian" in order to distinguish themselves from the right-wing advocates of libertarian capitalism.

Left libertarianism is defined a little differently by many European political scientists, in a usage introduced by Herbert Kitschelt in 1989. Left libertarian parties emphasise notions of internal party democracy and bottom-up participation. Green parties and radical left parties are often grouped together as "left-libertarian" parties by political scientists.

For political scientists Jan Jämte and Adrienne Sörbom,