This chapter examines climate policy efforts across six Spanish Autonomous Communities that joined the Under2 Coalition at different timepoints: founding member Catalonia, early joiners Basque Country and Foral Community of Navarre, and later joiners Andalusia, Community of Madrid, and Galicia. Operating within Spain’s multilevel governance system, these regions filled a policy vacuum created by limited national climate action at the national level prior to 2021. Catalonia demonstrates the clearest leadership profile, combining cognitive, entrepreneurial, and exemplary dimensions through pioneering legislation and transnational diplomacy. The Basque Country exhibits strong entrepreneurial orientation through sustained policy-based climate action, while Navarre shows entrepreneurial impulses undermined by implementation deficits. Among later joiners, Andalusia displays cognitive leadership rooted in two decades of strategic planning, Madrid remains comparatively incremental in its approach to climate policy despite economic capacity, and Galicia demonstrates increasing dynamism following strategically timed Under2 Coalition accession during COP 26. The analysis reveals that Under2 Coalition membership reinforced pre-existing leadership among founding and early members through reputational incentives, while its influence on later joiners appears to serve primarily to formalize existing commitments rather than catalyze transformation toward carbon neutrality.