How important are the remaining barriers to integration in international goods markets and how would eliminating them affect global and individual countries' welfare? This book studies these questions using the most comprehensive price data available. Bradford and Lawrence find that there is considerable market fragmentation among industrial countries -- that is, firms charging different prices for similar products in different national markets -- even among countries with low tariff barriers. The authors estimate that integration among the eight countries in their sample -- Australia, Canada, Germany, Italy, Japan, the Netherlands, the United Kingdom and the United States -- would raise global GDP by more than $500 billion, or about 2 percent. Remarkably, almost half the global gain in these eight countries could be reaped if Japan alone eliminated its international fragmentation.