Eco-certification of coffee, timber and other high-value agricultural commodities is increasingly widespread. In principle, it can improve commodity producers’ environmental performance, even in countries where state regulation is weak. However, evidence needed to evaluate this hypothesis is virtually nonexistent. To help fill this gap, we use detailed farm-level data to analyze the environmental impacts of organic coffee certification in central Costa Rica. We use propensity score matching to control for self-selection bias. We find that organic certification improves coffee growers’ environmental performance. It significantly reduces chemical input use and increases adoption of some environmentally friendly management practices.