The presentation will explain the way in which proportionality has permeated EU climate change law. Although presented as a fluid tool for rationalising and constraining EU and domestic legislation, and minimizing its burden on private operators’ economic rights, proportionality suffers from conceptual indecisiveness. Illustrative of this ambiguity is the relation between proportionality and necessity, which the EU political institutions present as conceptually distinct, but which the Court of Justice describes as being part of one same analysis. Proportionality has been particularly prevalent in the climate change institutional and due process provisions. The presentation will discuss the basic legal instruments falling under EU climate change law. After describing the proportionality provisions reflected in the Union’s main climate change legislative and regulatory acts and soft law instruments, comments will be made on the judicial interpretations of proportionality in the various climate change contexts that has been put to the attention of the Court of Justice. In conclusion the presentation will focus on some of the legal, constitutional and conceptual implications of the discrepancy between EU’s legislative and judicial practice.