The cooperative potential surrounding environmental problems suggests that the discussion of environmentally induced conflict and ecological insecurity has overlooked what may be a critically important corollary. Environmental cooperation could create positive externalities for international peace and human security by improving the climate of strategic interaction and political bargaining. This chapter evaluates the deductive case for environmental peacemaking, and discuses two separate hypothesized pathways. These are referred to as 'changing the strategic climate' and 'strengthening post-Westphalian governance'. In the environmental realm, both strategic and analytic uncertainty are pervasive, and both have inhibited international cooperation. The chapter examines four mechanisms by which certain forms of environmental cooperation might push an important dependent variable in a post-Westphalian direction. These mechanisms include the creation of new forms of interdependence, the fostering of new norms, the deepening of transnational civil society, and the transformation of governmental institutions in the direction of greater transparency and democratic accountability.