The social sector is undergoing a major transformation. We are witnessing an explosion in efforts to deliver social change, a burgeoning impact investing industry, and an unprecedented intergenerational transfer of wealth. Yet we live in a world of rapidly rising inequality, where social sector services are unable to keep up with societal need, and governments are stretched beyond their means. Alnoor Ebrahim addresses one of the fundamental dilemmas facing leaders as they navigate this uncertain performance measurement. How can they track performance towards worthy goals such as reducing poverty, improving public health, or advancing human rights? What results can they reasonably measure and legitimately take credit for? This book tackles three core challenges of performance faced by social enterprises and nonprofit organizations what to measure, what kinds of performance systems to build, and how to align multiple demands for accountability. It lays out four different types of strategies for managers to consider - niche, integrated, emergent, and ecosystem - and details the types of performance measurement and accountability systems best suited to each. Finally, this book examines the roles of funders such as impact investors, philanthropic foundations, and international aid agencies, laying out how they can best enable meaningful performance measurement.