Within the literature, climate change mitigation and adaptation at the local level is increasingly portrayed as a new, discrete field of spatial planning research and practice. This article examines in detail the situated institutionalization of this emerging field in lo-cal government in a specific case study context, Aarhus Municipality in Denmark. The concept of legitimacy is used as an analytical lens to examine institutionalization patterns and practices. Based on a perspective grounded in new institutional theory, the research investigates how legitimacy affects the institutionalization of climate change planning and how legitimacy is, in turn, affected by the interplay between agency and structure. The analytical foregrounding of the concept of legitimacy is concluded to generate ‘thicker’, more nuanced insights into why climate change planning practices take particular forms in specific contexts in terms of, for example, the role of networks external to local gov-ernment, and the form of mitigation and adaptation activities. The results highlight the importance of what we label cultural-cognitive legitimacy (i.e. that derived from organizational rules and societal norms) in determining patterns and practices of institutionalization, whereas normative imperatives based on moral or ethical arguments are rarely invoked in relation to legitimacy. This indicates that the role of structures vis-a-vis agency (particularly in terms of the often cited case of institutional entrepreneurship) in relation to the institutionalization of climate change planning within local government may be more complex than has been suggested much of the literature. The predominance of cultural-cognitive over normative legitimacy also has important implications for how dis-courses on climate change planning are framed. The implications of this for the nature of societal change that takes place in response to climate change require further research attention.
