Isaiah Berlin's celebrated radio lectures on six formative anti-liberal thinkers were broadcast by the BBC in 1952. They are published here for the first time, fifty years later. They comprise one of Berlin's earliest and most convincing expositions of his views on human freedom and on the history of ideas--views that later found expression in such famous works as "Two Concepts of Liberty," and were at the heart of his lifelong work on the Enlightenment and its critics. Working with BBC transcripts and Berlin's annotated drafts, Henry Hardy has recreated these lectures, which consolidated the forty-three-year-old Berlin's growing reputation as a man who could speak about intellectual matters in an accessible and involving way. In his lucid examination of sometimes complex ideas, Berlin demonstrates that a balanced understanding and a resilient defense of human liberty depend on learning both from the errors of freedom's alleged defenders and from the dark insights of its avowed antagonists. This book throws light on the early development of Berlin's most influential ideas and supplements his already published writings with fuller treatments of Helvétius, Rousseau, Fichte, Hegel, and Saint-Simon, with the ultra-conservative Maistre bringing up the rear. These thinkers gave to freedom a new dimension of power--power that, Berlin argues, has historically brought about less, not more, individual liberty. These lectures show Berlin at his liveliest and most torrentially spontaneous, testifying to his talents as a teacher of rare brilliance and impact. Listeners tuned in expectantly each week to the hour-long broadcasts and found themselves mesmerized by Berlin's astonishingly fluent extempore style. One listener, a leading historian of ideas who was then a schoolboy, was to recount that the lectures "excited me so much that I sat, for every talk, on the floor beside the wireless, taking notes." This excitement is at last recreated here for all to share.