Whether the European Union accedes to the European Convention on Human Rights is not a foregone conclusion, or at least not to the extent that it used to be in the period 2010-2014. Even though the accession remains a self-imposed obligation of the EU (Art. 6 (2) TUE), difficulties with gearing the Convention system to the EU’s specificity, especially after the convoluted Opinion 2/13 of the CJEU, might finally turn out too overwhelming for the Union – which currently needs to address much more urgent issues. Yet apart from the symbolic dimension of the accession (which still might rekindle some pro-European enthusiasm), this act, even viewed only from the theoretical point of view, offers a surprisingly innovative perspective of relations between international organisations and control systems of international human rights conventions. Among these relations issues related to international responsibility – and shared responsibility in particular – come to the fore. Attributing responsibility to the EU and/or its Member States after the accession is something of an uncharted territory. There exist general rules of law of international responsibility, there is case law of the ECtHR (and of the EComHR), but the exact norms governing attributing responsibility and co-responsibility in the case of the EU are not yet fully determined. Nevertheless, they might be of considerable importance for future development of law of international responsibility of IOs.