We estimate the impact of genetically modified (GM) crops on countrywide yields, harvested area, and trade using a triple-differences rollout design that exploits variation in the availability of GM seeds across crops, countries, and time. We find positive impacts on yields, especially in poor countries. Our estimates imply that without GM crops, the world would have needed 3.4 percent additional cropland to keep global agricultural output at its 2019 level. We also find that bans on GM cultivation have limited the global gain from GM adoption to one-third of its potential. Poor countries would benefit most from lifting such bans.