Cities must change rapidly to address a range of sustainability challenges. While urban experimentation has prospered as a framework for innovation, it has struggled to stimulate broader transformation. We offer a novel contribution to this debate by focusing on what municipalities learn from experimentation and how this drives organisational change. The practicalities of how municipalities learn and change has received relatively little attention, despite the recognised importance of learning within the literature on urban experiments and the central role of municipalities in enabling urban transformation. We address this research gap, drawing on four years of in-depth research coproduced with European municipal project coordinators responsible for designing and implementing the largest urban research and innovation projects ever undertaken. This cohort of professionals plays a critical role in urban experimentation and transformation, funnelling billions of Euros into trials of new solutions to urban challenges and coordinating large public-private partnerships to deliver them. For our respondents, learning how to experiment more effectively and embedding these lessons into their organisations was the most important outcome of these projects. We develop the novel concept of process learning to capture the importance of experimentation in driving organisational change. Process learning is significant because it offers a new way to understand the relationship between experimentation and urban transformation and should form the focus of innovation projects that seek to prompt broader urban transformation, rather than technical performance. We conclude by identifying implications for urban planning and innovation funding.