This has come up in C4SS, referencing a post in anti-libertarian blog Anti-Libertarian Criticism. Simpy put, the difference between left-libertarians and anarcho-capitalists is one of style, not substance. The left-libertarian definition of capitalism is exactly equal to the anarcho-capitalist (and also, increasingly, tea party) definition of corporatism, and the left-libertarian definition of free market is exactly equal to the anarcho-capitalist definition of capitalism. They both hold the so-called non-aggression principle not only as non-negotiable, but as the central feature of their ideology; the necessary and sufficient condition from which the rest of either left-libertarian or anarcho-capitalist theory can be derived.