Of all human qualities, humour is perhaps the most puzzling. Why do audiences laugh at catchphrases but don't laugh at jokes they have heard before? Why are words with a K in them generally found to be funnier? In this probing exploration, William Hartston interrogates every aspect of the evolution of humour and our attitudes toward it in hot pursuit of a Grand Unified Theory of Humour. From comedy in ancient Greece and jokes in ancient Rome, to laughter in the Bible and the secret of comic delivery, from how humour changed following the American Civil War, to the way Mark Twain influenced written comedy in the English-speaking world, William leaves no stone unturned in his quest to understand what makes us chuckle.