Most contemporary political philosophers take justice—rather than legitimacy—to be the fundamental virtue of political institutions vis-à-vis the challenges of ethical diversity. Justice-driven theorists are primarily concerned with finding mutually acceptable terms to arbitrate the claims of conflicting individuals and groups. Legitimacy-driven theorists, instead, focus on the conditions under which those exercising political authority on an ethically heterogeneous polity are entitled to do so. But what difference would it make to the management of ethical diversity in liberal democratic societies if legitimacy were prior to or independent from justice? This question identifies a widely underexplored issue whose theoretical salience shows how the understanding of what constitutes the primary question of political philosophy has a deep impact on how practical political questions are interpreted and addressed. What difference would it make, for example, whether the difficulties concerning the safeguard of human rights were couched in terms of the justice or of the legitimacy of the documents and treaties sanctioning their implementation. How should the issue of the quality of democracies be addressed whether one assigned priority to the justice or legitimacy of democratic institutions? Addressing these and other topical questions, the book offers a new theoretical angle from which to consider a number of pressing social and political issues. This book was previously published as a special issue of the Critical Review of Social and Political Philosophy.