This book discusses the idea of public justification as an approach to political legitimation in pluralistic societies. Public justification can be understood as the idea that political principles and institutions are legitimate only if they can be justified to all those subject to them. This apparently simple principle conceals a number of ambiguities, and raises the problem of how it could be realised in contemporary societies characterised by a variety of world-views and conceptions of the good. The book aims to clarify the idea of public justification, and argues that the work of some of the most prominent contemporary political philosophers can be understood as a response to the challenge of public justification. This argument is developed through a detailed analysis and critique of three contemporary theorists: John Rawls, Richard Rorty and Jurgen Habermas. The final chapter examines whether the idea of public justification can also provide a framework for thinking about problems of legitimation arising in the international context.