The economic theory of Preferential Trade Agreements (PTAs), or discriminatory trade liberalization for and among a subset ofnations, was first analyzed with fun damental and startling insight by Jacob Viner (1950). He destroyed the intuition that any move towards free trade was welfare-enhancing, for the country itself or for the world, or for both. He introduced us memorably to the notion of trade di verting -- and here, he meant not diversion in the old and approving sense of en tertainment but in the modern and castigating sense ofdistorting - Free Trade Ar eas (FTAs) and Customs Unions...