Social capital—the capacity of people to cooperate toward common aims—is an indispensable element in a free and prosperous society. Yet many studies show that social capital has been declining in many places in recent decades. Drawing on the work of scholars such as Robert Putnam, Francis Fukuyama, and Charles Murray, the authors describe social capital, demonstrate why it is important, and chart its decline. They also offer insight into the task of restoring it, a project that deserves the commitment of all those concerned about preserving what is good while building a better future.