Current responses to our most pressing societal challenges—from poverty to ethnic conflict to climate change—are not working. These problems are incredibly dynamic and complex, involving an ever-shifting array of factors, actors, and circumstances. They demand a highly fluid and adaptive approach, yet we address them by devising fixed, long-term plans. Social labs, says Zaid Hassan, are a dramatically more effective response. Social labs bring together a diverse a group of stakeholders—not to create yet another five-year plan but to develop a portfolio of prototype solutions, test those solutions in the real world, use the data to further refine them, and test them again. Hassan builds on a decade of experience—as well as drawing from cutting-edge research in complexity science, networking theory, and sociology—to explain the core principles and daily functioning of social labs, using examples of pioneering labs from around the world. He offers a new generation of problem solvers an effective, practical, and exciting new vision and guide.