This slim book does something difficult. Like a previous and somewhat dated literature, William Phelan's study analyzes a sui generis feature of the EU, but it studies this 'unidentified political object' in terms of a well-established International Relations literature on international regimes and legal interpretations on constitutionalization Phelan addresses the inherent problem of explaining a singular feature of the EU with a comparative analysis between WTO and other trade agreements Brexit has made Phelan's book an extremely topical study.