The recent proliferation of free trade areas and customs unions in the world trading system has led to an explosive revival of interest in the economic analysis of Preferential Trade Arrangements (PTAs). The principal theoretical question of the 1950s and 1960s (Viner) was whether PTAs would create or divert trade, causing welfare improvement or loss. The principal theoretical question (Bhagwati) of the late 1980s and 1990s has been whether PTAs encourage or discourage the worldwide nondiscriminatory freeing of trade. The essays in this volume present the central contributions to the analytical approaches developed to examine these questions.