There is a need to better understand the significance of NGOs in global environmental politics. Addressing a number of weaknesses in the current literature on NGOs, we have developed an analytical framework for analysis of NGO influence in international environmental negotiations. This paper demonstrates the utility of our framework by applying it to two cases: the negotiations of the Desertification Convention and of the Kyoto Protocol to the Climate Change Convention. We argue that the use of our research framework enables researchers to compare with confidence NGO influence across cases and that such comparison allows for a much needed examination of factors that explain variation in NGO influence in international environmental negotiations. Analysis of explanatory factors contributes to an improved understanding of the degree to which NGOs matter in global environmental policy-making.