A secular rise in volatility and uncertainty is overwhelming the capacities of conventional hierarchical governance and ‘command-and-control’ regulation in many settings. One significant response is the emergence of a novel, ‘experimentalist’ form of governance that establishes deliberately provisional frameworks for action and elaborates and revises these in light of recursive review of efforts to implement them in various contexts. Robust examples can be found in the United States and the European Union (EU) in domains ranging from the provision of public services such as education and child welfare to the regulation of food and air-traffic safety, and the protection of data privacy, as well as in transnational regimes regulating, for example, global trade in food and forest products. In this chapter we analyze the properties of these experimentalist governance processes, and show how their distinctive mechanisms for accountability, monitoring, and compliance enforcement respond to the demands of a world in which precise policy goals and methods of achieving them cannot be determined ex ante, but must instead be discovered in the course of problem-solving. By way of conclusion, we contrast conventional and experimentalist governance approaches to the problem of power disparities, and discuss the distinctive way experimentalist reforms aim to overcome such structural barriers to change.