Why do OECD countries vary in their regulatory approach towards non-governmental organizations (NGOs)? This paper introduces an index to assess NGO regulation regarding barriers to entry, NGOs’ political capacity, and economic activity. Our cross-section analysis of 28 OECD countries offers preliminary evidence of systematic differences in NGO regulation between corporatist and pluralist systems. We suggest corporatist systems have more restrictive regulations because NGOs risk upsetting the political order and managed social consensus. In pluralist countries, NGOs face fewer restrictions because governments view them as substitutes for formal communication channels. We present two cases, Japan (corporatist) and the United States (pluralist), to illustrate this argument. In sum, macro-institutional arrangements of political representation have a crucial bearing on national styles of NGO regulation. Future uses of this index include examining the effects of national context on international NGOs, explaining variations in organizational structures and strategies among NGOs, and tracking variations in NGO-state relations over time.