ROY PORTER WAS a friend of mine. We studied at the same Cambridge college, specialised in the same period (the eighteenth century) and, when it came time to leave Cambridge, each found a home in London, he at University College, I at King’s. But there the similarities end; for, although I have spent the past thirty years producing a modest total of books, films and papers, Roy was tirelessly productive. The endpapers of this book, reprinting sections of obituaries, speak of him as ‘inexhaustible’ (Guardian) , ‘indefatigable’ (Sunday Times) and ‘superhuman’ (London Review of Books). The text of the book was completed just a week before he died and represents his final statement on medical history – the subject that he had made his own.