Climate adaptation is a growing imperative across all scales and sectors of governance. This often requires changes in institutions, which can be difficult to realize.Explicitly process-oriented approaches explaining how and why institutional change occurs are lacking. Overcoming this gap is vital to move beyond either input-oriented (e.g., capacity) or output-oriented (e.g., assessment) approaches, to understand how changes actually occur for addressing complex and contested governance issues. This paper analyses causal conditions and mechanisms by which institutions develop in climate adaptation governance. It focuses on urban climate governance through an in-depth case study of Santiago, Chile, over a 12-year period (2005-2017), drawing on primary and secondary data, including 26 semistructured interviews with policy, academic, and civil society actors. It identifies and explains a variety of institutional developments across multiple levels (i.e., programmatic, legislative, and constitutional), through a theory-centric process tracing methodology. This reveals a multiple-response pattern, involving several causal mechanisms and coexisting institutional logics. Findings suggest that although adaptation may be inherently protracted, institutions can nevertheless develop in both related and novel directions.Overall, the paper argues for a new research agenda on process-oriented theorizing and analysis in climate and environmental governance.