The Introduction previews how population density and competition drive the strategies of INGO leaders and entrepreneurs. Our approach provides an explanation for three important but puzzling trends in the population of American INGOs. First, fewer INGOs are being created even though unmet needs remain substantial and available resources are steady if not increasing. Second, INGOs are becoming narrower in their missions even though global issues are arguably becoming more complex and interconnected. And third, INGOs are increasingly dispersing their activities globally, avoiding “crowded” areas, even though concentrating efforts in areas of acute need may be more efficient or just. We argue that existing scholarship has not yet examined or explained these consequential developments. We conclude by offering an overview of the book’s methods and chapter content.