This paper examines the strategic nature of choice of environmental standards under different degrees of openness of countries. It also compares and contrasts equilibrium environmental standards and levels of pollution, local and global, with the world optimum levels. It shows that, in case of open economies, environmental standards can be strategic substitutes or complements. In equilibrium, countries set higher environmental standards in case of open economies compared to that in case of closed economies. It also shows that equilibrium standards in case of open economies are higher than the world optimum in certain situations. In contrast, countries set lower environmental standards, in equilibrium, than the world optimum in absence of international trade.