The aim of this article and the ensuing Special Issue is to assess, après fifteen years, the effects on the EU legal and political system of the overhaul of executive delegated powers inaugurated by the Lisbon Treaty. It identifies core parameters – i.e. (institutional) balance of powers, (democratic) legitimacy, control and accountability, effectiveness of EU policy implementation – considered by the contributions to this Special Issue to map and examine, both constitutionally and normatively, the EU system of delegated powers in law and practice. It also puts forward seven overarching reflections revealing some of the core issues and challenges posed by the current stage of development of the post-Lisbon EU system of delegated powers.