Public administration, business management, international relations, and other fields of scholarship and practice are converging around a new mode of governance: cross-sector collaboration to meet social challenges. At levels from local to global, governments, businesses, and civil society organizations are experimenting with new ways of partnering, and scholars are offering new analyses and recommendations. This chapter explores this rapidly growing phenomenon: what is meant by collaborative governance, why it is happening, and the state of scholarship on the topic. The author finds that collaborative governance has the potential to contribute greatly to the large-scale social transformations needed to address humanity’s most compelling challenges. But although considerable progress has been made in understanding when and why collaborative approaches emerge and how they function, much remains to be done to improve and scale up practice and to evaluate the impact of collaborative governance efforts. The chapter ends with a call for a scaled-up research agenda in keeping with the scale, promise, and potential pitfalls of this major social innovation.