Abstract. We analyze the role of National Treatment in the regulation of environmental product standards for an open economy. A social planner uses product standards to control emissions from the consumption of a traded good. We show that whether National Treatment of standards interferes with welfare-maximizing policy depends on the instruments available to the policy maker (consumption or emissions tax) and differences in the cost of complying with the standard. We also highlight the asymmetric incidence of the domestic and import product standard when taxes are suboptimal. This asymmetric incidence can also cause welfare-maximizing policy to violate National Treatment.