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2 Although previous work largely suggests that non-governmental organizations (NGOs) might have a positive impact on international environmental negotiations to the extent that states in turn are more likely to agree on stronger environmental commitments, the empirical evidence is unclear. In order to address this shortcoming, this article firstly employs a spatial bargaining model, which demonstrates that NGOs primarily help states facilitating information problems in negotiations. The authors then analyze quantitative data on international environmental regimes and find evidence that NGOs do indeed positively influence environmental treaty negotiations. More specifically, the stronger the engagement of those civil-society actors and the more NGOs are effectively involved during negotiations, the higher the degree of regime members ’ commitment, i.e., their depth of cooperation afterwards. Finally, the theory on those variables implies that the impact of NGO pressure on state commitment levels should vary conditional on the number of NGOs involved. The paper finds evidence for this interaction, although the results go against conventional wisdom