Cities are key in urban climate mitigation. Since the early 2000s, a trend of urban climate governance experimentation has been observed in which cities, and especially city governments, are trialing novel governance interventions, processes, and instruments to learn from their development and implementation. This article explores the role of the government of the city of Seoul, South Korea, in a range of local experiments. It particularly focuses on the factors that contribute to the success (or lack thereof) of urban climate governance experimentation. It finds that the city's government has been successful in developing and trialing some but not all experiments and that the overall results of these are promising in certain areas of city development and use. The article also highlights some less promising results, indicating the fragile nature of urban climate governance experimentationï¿½in both the scientific and political senses of the term.