The European Securities and Markets Authority (ESMA) is the only EU agency with the powers to exercise all three stages of enforcement, i.e. monitoring; investigating; and sanctioning. At the same time, it may need to look to Member States’ authorities for assistance in the exercise of its enforcement powers. While this means that tasks can be shared, this chapter shows that the national authorities always stand in a subordinate relationship to ESMA; ESMA remains the responsible actor. This is good news in terms of accountability: the legislative framework is clear as to the allocation of responsibility in the shared enforcement system towards credit rating agencies and trade repositories. ESMA’s accountability framework thus reveals no significant gaps and therefore gets the best rating: ‘AAA’ status.