Isaiah Berlin is a towering figure in the world of letters. To the international community of scholars he is best known as the author of Two Concepts of Liberty, yet his career covers many fields in addition to moral and political philosophy: music and literary criticism, historiography, scholarship in the history of ideas, cultural interpretation, translation, teaching, university and arts administration, diplomacy, community work, and broadcasting.This is the first systematic study of Berlin's political ideas to draw on all of his writings, including manuscripts, interviews, and correspondence. Berlin's defence of political liberalism is based on moral pluralism and an interpretation of the historical and cultural development of western civilization, rather than on abstract arguments about rights. Claude Galipeau brings out the uniqueness and force of this defence while acknowledging, in his discussion of Berlin's Zionism, the tensions and complexities inherent in it.In all his writings Berlin seeks to understand the intricacies and paradoxes of human behaviour. His political thought offers a compelling justification of liberal institutions in the contemporary world and Claude Galipeau's study will be an invaluable guide to the range and depth of his work.