We develop a North-South model of international trade and transboundary pollution to analyze the relationship between environmental technology transfer and the South's incentive to join an international environmental agreement (IEA). We find necessary and sufficient conditions under which technology transfer will increase the South's incentive to join the IEA. We also find necessary and sufficient conditions under which the South's participation in the IEA will increase the market incentive for technology transfer. Results have clear policy implications for (i) the sequence of technology transfer and the South's IEA membership, and (ii) the legitimacy of the South's subsidies for technology transfer. Copyright © 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd.