Isaiah Berlin was one of the leading political thinkers of the twentieth century, and his work continues to attract admiration and debate. In Isaiah Berlin: Liberty, Pluralism and Liberalism, George Crowder provides both an accessible introduction to Berlina s ideas and an original contribution to political theory. Berlina s range of interests and learning was vast but united by a single overarching project: the uncovering of the conceptual roots of twentieth--century totalitarianism. He traces these through three levels of analysis: the distortion of the concept of freedom by thinkers such as Rousseau, Fichte, Hegel and Marx; the scientism of the Enlightenment and irrationalism of the Counter--Enlightenment and romanticism; and moral monism, the idea that all ethical questions can be answered by reference to a single moral law. Against monism, Berlin asserts the claims of value pluralism, which he aligns with a politics of liberal moderation. In this new assessment, Crowder argues that Berlina s critique of the modern enemies of liberty is exciting and powerful, but also that the coherence of his thought is threatened by a tension between its liberal and pluralist elements. Crowder goes on to suggest how that tension can be resolved by appeal to arguments that go beyond the case actually presented by Berlin but which remain within the spirit of his general outlook.