Civil society organizations, nonprofits, national and international nongovernmental organizations, and a variety of formal and informal associations have coalesced into a world political force. Though the components of this so-called third sector vary by country, their cumulative effects play an ever-greater role in global affairs. Looking at relief and welfare organizations, innovation organizations, social networks, and many other kinds of groups, Meghan Elizabeth Kallman and Terry Nichols Clark explore the functions, impacts, and composition of the nonprofit sector in six key countries. Chinese organizations, for example, follow the predominantly Asian model of government funding that links their mission to national political goals. Western groups, by contrast, often explicitly challenge government objectives, and even gain relevance and cache by doing so. In addition, Kallman and Clark examine groups in real-world contexts, providing a wealth of political-historical background, in-depth consideration of interactions with state institutions, region-by-region comparisons, and suggestions for how groups can borrow policy options across systems. Insightful and forward-seeing, The Third Sector provides a rare international view of organizations and agendas driving change in today’s international affairs.