This article provides a "top-down" explanation for the rapid growth of nongovernmental organizations (NGOs) in the postwar period, focusing on two aspects of political globalization. First, I argue that international political opportunities in the form of funding and political access have expanded enormously in the postwar period and provided a structural environment highly conducive to NGO growth. Secondly, I present a norm-based argument and trace the rise of a pro-NGO norm in the 1980s and 1990s among donor states and intergovernmental organizations (IGOs), which has actively promoted the spread of NGOs to non-Western countries. The article ends with a brief discussion of the symbiotic relationship among NGOs, IGOs, and states promoting international cooperation.