As far as local governments are responsible for the practical implementation of many European Union (EU) policies, they codetermine member states’ EU compliance records and the fate of EU legislation. Yet, they do so in remarkably different ways, as exemplified by the variegated implementation of the Ambient Air Quality Directive 2008/50/EC by Dutch municipalities. Taking guidance from the literature on EU compliance, in this article we explain the differences in local implementation performance based on the political and managerial approaches. Understanding which of the two approaches drives different local responses to EU policy bears consequences for the appropriate remedy for nonimplementation. Four municipalities were purposefully selected along with the two-by-two implementation performance scoring matrix in the realm of air quality. A comparative within-case analysis specifies how political explanations outweigh managerial explanations in accounting for variation in implementation performance and distils ‘policy saliency’ as the driving causal mechanism.