'I was exhausted at the end,&yet I am sure that if ever I saw&heard anyone in a true state of inspiration it was then.'

So wrote a listener to her friend after attending one of the lectures based on the book.Political Ideas in the Romantic Ageis the text Berlin wrote for four of the lectures, delivered in 1952. He revised what he had written extensively afterwards but never published it. It is his longest work and also the only connected account he gave of his key insights into the history of the ideas that dominate the political arguments of our own time.

As he put it in his Prologue, 'The age of which we speak was singularly rich in original conceptions; they transformed our world, and the words in which they were formulated speak to us still'.

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.

Isaiah Berlin's longest continuous work - and therefore of key importance to anyone interested in the history of ideas.