Robert Nozick's Anarchy, State, and Utopia (1974), along with John Rawls's A Theory of Justice (1971), radically changed the landscape in analytic political philosophy. For much of the preceding half-century, under the influence of logical positivism's heavy emphasis on empirical verifiability, much of moral philosophy was taken up with metaethics (e.g. the semantics of moral discourse), with little attention given to normative moral theories. Moreover, to the extent that normative theories were considered, utilitarianism was the centre of attention. This all changed with the publication of Rawls's articulation and defence of liberal egalitarianism and Nozick's libertarian challenge to the legitimacy of anything more than the night-watchman state.

At the core of Nozick's book are two arguments. One is that a night-watchman state (which protects only against violence, theft, fraud and breach of contract) could be legitimate, even without the consent of all those to be governed. The other is that nothing more extensive than the night-watchman state is legitimate, except with the consent of all. The argument is complex, and Nozick often inserts long – and very interesting – digressions. Below I shall focus only on his core argument. I shall thus not address his discussions of Rawls's theory of justice (ch. 7, § 2) and other arguments attempting to justify more than the night-watchman state (ch. 8), nor his discussion of utopias (ch. 10).