Isaiah Berlin's celebrated radio lectures on six important anti-liberal thinkers were delivered on the BBC's "Third Programme" in 1952. They are published here for the first time, 50 years on. "Freedom and its Betrayal" is one of Isaiah Berlin's earliest and most convincing expositions of his views on human freedom and the history of ideas, views which later found expression in such works as "Two Concepts of Liberty", and were at the heart of his lifelong work on the Enlightenment and its critics. In his examinations of sometimes difficult ideas, Berlin demonstrates that a balanced understanding and a resilient defence of human liberty depend on learning both from the errors of freedom's defenders and from the dark insights of its antagonists. This book throws light on the early development of Berlin's ideas, and supplements his already published writings with fuller treatments of Helvetius, Rousseau, Fichte, Hegel and Saint-Simon, with the ultra-conservative traditionalist Maistre bringing up the rear. It shows Berlin at his liveliest and most torrentially spontaneous, testifying to his talents as a teacher of rare brilliance and impact.