On April 5th 2013, the draft agreement on the European Union accession to the European Court of Human Rights was finalized. The agreement identifies the reasons for the accession and underlines the legal and political obstacles that the negotiation process had to overcome, mainly to be attributed to the EU's unique nature and complex internal organization. Particular attention is devoted to the concept of external autonomy of the Union, stressing that the accession to the ECHR cannot weaken this basic principle. The agreement tries to spell out the implications of external autonomy in the interplay between the two European courts and to explain the complex procedural mechanisms introduced to guarantee its respect. These include the Co-respondent Mechanism and the Prior Involvement of the European Court of Justice when, in the lack of reference for a preliminary ruling from the national judge, this has not had a chance of deciding on the violation of one of the Convention's rights, before the claim is brought before the ECHR.