There are multiple estimates of global monetary and multidimensional poverty, but there are still no estimates of populations at risk of social exclusion worldwide. This paper fills this gap by estimating the share and number of populations at risk of exclusion globally and regionally. It develops a conceptual framework of social exclusion that builds on Sen’s capability approach and emphasizes the relative, multidimensional, and dynamic features of exclusion. The paper also develops a macro counting measure of population groups that are particularly vulnerable to exclusion based on identity, circumstances, and socioeconomic conditions. The empirical strategy surveys the most reliable sources of vulnerable populations across countries and develops a protocol to avoid double-counting of individuals at risk of social exclusion. Overall, between 2.33 billion and 2.43 billion people—roughly 32 percent of the global population—are estimated to be at risk of being socially excluded. The South Asia and East Asia and Pacific regions contain 1.3 billion such people, with India and China alone home to 840 million of them. Meanwhile, 52 percent of Sub-Saharan Africa’s population is vulnerable to exclusion, the greatest share of any region. The paper also discusses several implications of these estimates, emphasizing that policies targeting the poor might not be sufficient to tackle social exclusion.