Few virtues are as celebrated in contemporary culture as openness. Rooted in software culture and carrying more than a whiff of Silicon Valley technical utopianism, openness - of decision-making, data, and organizational structure - is seen as the cure for many problems in politics and business. But what does openness mean, and what would a political theory of openness look like? With Wikipedia and the Politics of Openness, Nathaniel Tkacz uses Wikipedia, the most prominent product of open organization, to analyze the theory and politics of openness in practice - and to break its spell. Through discussions of edit wars, article deletion policies, user access levels, and more, Tkacz enables us to see how the key concepts of openness - including collaboration, adhocracy, and the splitting of contested projects through "forking" - play out in reality. The resulting book is the richest critical analysis of openness to date, one that roots media theory in messy reality and thereby helps us move beyond the vaporware promises of digital utopians and take the first steps toward truly understanding what openness does, and does not, have to offer.