We have seen a worldwide increase in new nonstate, multi-stakeholder organizations setting standards for socially and environmentally responsible behavior. These standard-setting arenas offer new channels for political participation for NGOs. Scholars have drawn attention to the rise and the role of NGOs in global politics, but there is less research on the power and long-term implications of NGO participation in transnational multi-stakeholder standard-setting. This article analyzes NGOs within three such global organizations: the Forest Stewardship Council, the Marine Stewardship Council, and the International Organization for Standardization on Social Responsibility. Using a power-based perspective, we demonstrate the impact that NGOs can have on multi-stakeholder work. In doing so, we analyze four types of NGO power: symbolic, cognitive, social, and monitoring power. The article further emphasizes institutional, structural, and discursive factors within multi-stakeholder organizations that create certain challenges to NGO power and participation in the longer term. (c) 2010 by the Massachusetts Institute of Technology.