Abstract: This book explores organized labor’s role in the rapid trade liberalization pursued by developing countries since the 1980s. It argues that labor unions opposed liberalization, and where labor rights were well protected, they effectively slowed down the rate of trade policy reform. Labor unions were particularly influential when democratization opened up public debates about economic policy. Unions called general strikes and pushed back against the liberalization demands of export-oriented businesses and pro-reform technocrats. Such labor opposition also blunted the effectiveness of international demands for liberalization, which came most importantly from the United States. However, labor unions failed to influence trade policy in countries where workers’ rights were less protected. When countries democratized but did not protect workers’ rights, liberalization proceeded rapidly. Similarly, the United States’ efforts to open markets were more successful when focused on developing countries that lacked powerful unions. In short, where unions were granted a voice in policy debates they managed to push back against both domestic and international demands for free trade. This book supports these arguments with quantitative analysis of data from 121 developing countries from 1985 to 2010, including original data gathered from the United States Trade Representative’s annual National Trade Estimate report, as well as qualitative case studies of trade reform in India, Bolivia, and Argentina. This paper advances our understanding of the domestic politics of trade, and is also the first to present systematic quantitative evidence of international pressure leading to trade liberalization.