Abstract: An economist who talks about unified theory to lawyers and social scientists gets welcomed rather like the British expedition to Afghanistan in 1840. The Afghanistanis preferred to fight rather than join the British empire, and many social scientists are similarly disposed towards the economics empire. Like the nineteenth-century British, however, economics imperialism has succeeded remarkably. Economic models of rational behaviour have affected all the social sciences in the last thirty years, as well as history, philosophy, and law. Everyone in social science, whether friend or foe of economics, should want to understand its success.