Environment and trade are increasingly linked through preferential trade agreements. Despite the encompassing nature of environmental provisions in trade agreements, studies on causes and consequences of the trade and environment linkage are scarce. A main cause hindering research in this area is the lack of data. In this research note, we introduce an original data set (TREND) on environmental provisions found in 630 trade agreements signed between 1947 and 2016—the most comprehensive data set in terms of both variables coded and agreements covered. We illustrate the data set’s usefulness by assessing the question of why countries include environmental provisions in trade agreements. Are trade negotiations opportunities to promote stringent environmental standards? Or are environmental provisions window dressing covering protectionist interests? We find evidence that democracies, countries that face import competition, and countries that care about the environment are more likely to include environmental provisions in trade agreements. The database is of particular relevance for research on international institutional design, policy innovation, regime complexity, policy diffusion, and regime effectiveness.