'By integrating key concepts such as population density from organizational ecology to International Relations, Bush and Hadden offer a fresh perspective on the evolution of the non-profit sector both in the US and globally. Their meticulous research provides insightful answers to fundamental questions, such as why certain organizations lean toward hyper-specialization and under what conditions NGOs are more likely to compete with, rather than collaborate with, like-minded organizations in crucial areas of global governance.' Alexander Cooley, Barnard College, Columbia University