‘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 Age is 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’.