In his final, wide-ranging book, Gerald Gaus critically reexamines Hayek's analyses. Drawing on diverse work in social and moral science, Gaus argues that Hayek's program was manifestly prescient and strikingly sophisticated, always identifying real and pressing problems. Yet, Gaus maintains, Hayek underestimated the resources of human morality and the Open Society to cope with the challenges he perceived. Gaus marshals formal models and empirical evidence to show that our Open Society is grounded on moral foundations of human cooperation originating in our distant evolutionary past, but has built upon them a complex and diverse society that requires us to rethink both the nature of moral justification and the meaning of democratic self-governance. In these fearful, angry and inwardly-looking times, when political philosophy has itself become a hostile exchange between ideological camps, The Open Society and Its Complexities shows how moral and ideological diversity, so far from being the enemy of a free and open society, can be its foundation.