While media attention focuses such famous philanthropists as Bill Gates and Charles Koch, thousands of donors are at work below the radar promoting a wide range of causes, including education, the environment, science, and LGBT rights. Charting the rise of these powerful individuals, David Callahan shows how the fortunes of a second Gilded Age are being used to shape American life in ways both good and bad. As new waves of billionaires like Mark Zuckerberg turn to philanthropy, Callahan projects how this may affect our society in the decades to come.