This article examines three constitutional environmental provisions and how they have been applied by courts in Europe in three climate cases from Norway, Germany and France. In each of these cases, directive principles, that is, constitutionally entrenched state obligations to protect social values, generally by enacting legislation, played a key role in judicial decisions regarding climate change mitigation. We engage with Lael K. Weis’s analytical framework on directive principles to clarify the allocation of institutional responsibility for climate change mitigation as applied in these three cases, and argue that clarifying these roles alleviates some of the criticism regarding the democratic legitimacy of judicial decision making on climate change. Importantly, while courts do not directly enforce these types of constitutional directive principles, they must adjudicate them. When courts interpret constitutionally mandated legislation in light of directive principles, they develop new constitutional environmental norms. While most scholarly analysis of environmental constitutionalism has focused on environmental rights, our examination confirms Weis’s thesis that directive principles aimed at legislatures are also important forms of environmental constitutionalism, and deserving of further attention.