It’s not easy to talk about left-libertarianism. These days most people still associate libertarianism with the right, and the fact that most left-libertarians identify as anarchist must confuse those not too aware of political philosophy; one might think that think left-libertarians are another kind of collectivist anarchists. I would to start by quoting perhaps the most well-known left-libertarian alive, Sheldon Richman, who was a fellow at several libertarian think-tanks and whose articles are reprinted by both Reason and CounterPunch. Curiously enough his most didactic article on left-libertarianism appeared at The American Conservative:
Left-libertarians favor worker solidarity vis-à-vis bosses, support poor people’s squatting on government or abandoned property, and prefer that corporate privileges be repealed before the regulatory restrictions on how those privileges may be exercised. They see Walmart as a symbol of corporate favoritism—supported by highway subsidies and eminent domain—view the fictive personhood of the limited-liability corporation with suspicion, and doubt that Third World sweatshops would be the “best alternative” in the absence of government manipulation.
Obviously radical statements like that don’t sound like the usual “free market” reforms that some people promote in the GOP, not even something that one could hear from libertarian institutions like the Cato Institute. It’s is probably the complex history of the libertarian movement that is most useful in explaining left-libertarianism. The libertarian story is long and had a particular relation to American history. I still recommend the marvelous Radicals for Capitalism of Brian Doherty, to these the day the most complete history of the American libertarian movement, readers could be surprised to know that despite its name, Doherty devoted a long part of the book to the left-libertarian writer Karl Hess. Another very interesting work is History of the Libertarian Movement by Samuel Edward Konkin, obviously like all of his writings it was from a more left-libertarian perspective.
The most common point of origin left-libertarians point to is the precursors of libertarianism, sometimes called proto-libertarianism. The nineteen century had several radical individualist anarchists that were in favor of free markets, including thinkers like Lysander Spooner, Benjamin Tucker and Voltarine de Cleyre. Then in twentieth century the New Left-Old Right alliance that Murray Rothbard proposed in the context of the opposition to the Vietnam War was vital for the development of left-libertarianism. Probably the most known left-libertarians of this period is Karl Hess, the Goldwater speechwriter turned Black Panther ally, the National Review founder who wrote legendary manifesto The Death of Politics at Playboy, the man that leave the American Enterprise Institute for the Institute of Policy Studies, from working for the RNC to be an SDS activist.