This paper examines the extent to which environmental groups cooperate globally. The literature on international environmentalism has increasingly stressed the development of cooperative networks among environmental NGOs, the sharing of environmental information and resources, and the development of a global civil society within the environmental movement. We determine the actual extent of this global environmental network, and the implications for international environmentalism. We examine the responses of 248 environmental groups included in the 1998 Global Environmental Organizations Survey (GEOS). The responses to our questions yield valuable insights into the extent to which groups cooperate nationally and internationally, and the nature of this cooperation. In addition, we provide an initial explanation for the crossnational variation in groups' responses to our questions.