The question of exactly who benefits from the Treaties, in the sense of which range of persons and bodies should be recognised as legally competent to enforce any given provision of Union law before the national courts, is surprisingly murky. This lack of clarity is due partly to the inherent complexity of the question, as well as to the complication posed by the interdependent relationship between the Union and national legal orders. The confusing approach adopted by the Court of Justice compounds the matter. This chapter discusses some observations on why this is a question which poses particular policy challenges for the Union legal order, before going on to summarise the relevant tools employed by the Court of Justice when addressing issues about the decentralised enforcement of Union law by private and public actors. It is argued that, despite the apparent confusion, it is possible to construct a workable division of labour between the role of Union law in defining its own protective scope (on the one hand) and the discretion of each Member State over access to the courts for the enforcement of Union law (on the other hand). A detailed analysis of the case law is conducted in order to identity the weakest links in the system, or at least those which suffer from the greatest degree of doctrinal and conceptual neglect. The question of who exactly benefits from the Treaties, in the sense of enjoying rights of standing to enforce Union law before the national courts, presents both surprisingly difficult challenges and promising research issues for the future.