Isaiah Berlin's celebrated radio lectures on six formative anti-liberal thinkers were delivered on the BBC's Third Programme in 1952. They are published here for the first time, fifty 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 famous works as 'Two Concepts of Liberty', and were at the heart of his lifelong work on the Enlightenment and its critics.

In his lucid 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 alleged defenders and from the dark insights of its avowed antagonists. This book throws light on the early development of Berlin's ideas, and supplements his already published writings with fuller treatments of Helvétius, Rousseau, Fichte, Hegel and Saint-Simon, with the ultra-conservative traditionalist Maistre bringing up the rear.

Freedom and its Betrayalshows 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 broadcasts and found themselves mesmerised by Berlin's astonishingly fluent extempore style. A leading historian of ideas, who was then a schoolboy, records 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.

Isaiah Berlin was born in Riga, now capital of Latvia, in 1909. When he was six, his family moved to Russia, and in Petrograd in 1917 Berlin witnessed both Revolutions - Social Democratic and Bolshevik. In 1921 he and his parents emigrated to England, where he was educated at St Paul's School, London, and Corpus Christi College, Oxford. Apart from his war service in New York, Washington, Moscow and Leningrad, he remained at Oxford thereafter - as a Fellow of All Souls, then of New College, as Chichele Professor of Social and Political Theory, and as founding President of Wolfson College. He also held the Presidency of the British Academy.

His published work includesKarl Marx, Russian Thinkers, Concepts and Categories, Against the Current, Personal Impressions, The Sense of Reality, The Proper Study of Mankind, The Roots of Romanticism, The Power of Ideas, Three Critics of the Enlightenment, Freedom and Its Betrayal, Liberty, The Soviet MindandPolitical Ideas in the Romantic Age. As an exponent of the history of ideas he was awarded the Erasmus, Lippincott and Agnelli Prizes; he also received the Jerusalem Prize for his lifelong defence of civil liberties. He died in 1997.

'Never before had someone addressed such abstract topics with such fluency and intensity - these lectures, while presupposing no specialist expertise, introduce some of the key issues in modern political theory in an enthusiastic and quite unpatronising way' Noel Malcolm, Sunday Telegraph