Megacity disaster risk governance is a burgeoning interdisciplinary field that seeks to encourage improved public decision-making about the safety and sustainability of the world’s largest urban centers in the face of environmental threats ranging from floods, storms, earthquakes, wildfires, and pandemics to the multihazard challenges posed by human-forced climate change. It is a youthful, lively, contested, ambitious and innovative endeavor that draws on research in three separate but overlapping areas of inquiry: disaster risks, megacities, and governance. Toward the end of the 20th century, each of these fields underwent major shifts in thinking that opened new possibilities for action. First, the human role in disaster risks came to the fore, giving increased attention to humans as agents of risk creation and providing increased scope for inputs from social sciences and humanities. Second, the scale, complexity, and political–economic salience of very large cities attained high visibility, leading to recognition that they are also sites of unprecedented risks, albeit with significant differences between rapidly growing poorer cities and slower growing affluent ones. Third, the concept of public decision-making expanded beyond its traditional association with actions of governments to include contributions from a wide range of nongovernmental groups that had not previously played prominent roles in public affairs. At least three new conceptions of megacity disaster risk governance emerged out of these developments. They include adaptive risk governance, smart city governance, and aesthetic governance. Adaptive risk governance focuses on capacities of at-risk communities to continuously adjust to dynamic uncertainties about future states of biophysical environments and human populations. It is learning-centered, collaborative, and nimble. Smart city governance seeks to harness the capabilities of new information and communication technologies, and their associated human institutions, to the increasingly automated tasks of risk anticipation and response. Aesthetic governance privileges the preferences of social, scientific, design, or political elites and power brokers in the formulation and execution of policies that bear on risks. No megacity has yet comprehensively or uniformly adopted any of these risk governance models, but many are experimenting with various permutations and hybrid variations that combine limited applications with more traditional administrative practices. Arrangements that are tailor-made to fit local circumstances are the norm. However, some version of adaptive risk governance seems to be the leading candidate for wider adoption, in large part because it recognizes the need to continuously accommodate new challenges as environments and societies change and interact in ways that are difficult to predict. Although inquiries are buoyant, there remain many unanswered questions and unaddressed topics. These include the differential vulnerability of societal functions that are served by megacities and appropriate responses thereto; the nature and biases of risk information transfers among different types of megacities; and appropriate ways of tackling ambiguities that attend decision-making in megacities. Institutions of megacity disaster risk governance will take time to evolve. Whether that process can be speeded up and applied in time to stave off the worst effects of the risks that lie ahead remains an open question.