John Stuart Mill's thought has been central in recent (as well as older) works of political theory discussing the relationship between liberal democratic politics and nationality or nationalism -- which is far from surprising, given his undisputed influence on liberal attitudes towards nationality from the 1860s to the present. This book provides the first thorough critical study of the attitude of this pillar of the liberal tradition towards nationality, nationhood, patriotism, cosmopolitanism, intervention/non-intervention, and international politics more generally. Based on exhaustive research in a great range or writings by Mill, as well as by his contemporaries and later students, it establishes for the first time clearly and subtly where exactly Mill stood with regard to nationhood, nationalism, patriotism, cosmopolitanism, national self-determination, intervention/non-intervention and other important issues in international ethics. It thus exposes and challenges all sorts of misconceptions, half-truths, or myths surrounding Mill's views on, and attitude towards, nationality and related issues in a vast literature from the mid-nineteenth to the beginning of the twenty-first century. At the same time, it offers a timely contribution to contemporary debates among political theorists on the relationship between liberal democratic values and nationalism, patriotism and cosmopolitanism, not least through its articulation of a distinct sense in which patriotism and cosmopolitanism can be compatible and mutually reinforcing (based on Varouxakis's interpretation of Mill's thought on this question). The reader will find critical discussions of the pronouncements on some of the issues examined (or on Mill's contributions to them) of some of the most important late-twentieth-century political theorists as well as of contemporaries or near-contemporaries of Mill.