Over the last decade, a growing body of academic literature has reflected on how and under which conditions experiments in global climate governance lead to broader changes in rules, norms, and practices helping to meet the challenge of climate change. Drawing on the assumptions of the scholarship on experimentalist governance architectures, this article analyzes the effectiveness of the Covenant of Mayors (CoM) as a comprehensive governance framework that enables the development and coordination of local policies for sustainable energy and climate through a range of joint instruments for recursive goal setting, monitoring, and benchmarking. Our findings illustrate the CoM’s significant potential in terms of both general political uptake and policy output, which could make of this program, if appropriately fine-tuned, a successful governance experiment contributing to building a more effective global climate regime.