The European Union is unique among jurisdictions in having constitutionalized its policy goals and methods, by embedding these in the Treaties. As a result, the legislature is far more constrained in its activities than is the case in other constitutional orders. Yet the Treaties are indeterminate, and it is the Court of Justice which interprets and delimits them, and instructs the legislature on how and to what extent it may pursue them. There is, in substance, a principal–agent relationship between the Court and the EU legislature, enforceable by the Court's capacity to annul legislation contrary to its preferences. An examination of internal market legislation shows that indeed it consists of codification of prior case law. The judicial constraints on the EU legislature are sufficiently tight that the legislature is more akin to a subordinate implementing regulator than to an autonomous political policy‐maker.