This work started life as a doctoral research project exploring one of the apparent transatlantic divergences that continue to exist within competition law, namely the differing approaches to the issue of a regulated margin squeeze adopted by the EU and US antitrust systems. It soon became clear, however, that the concurrent application of competition law and economic regulation is merely a single aspect of their broader interrelationship. Thus, the focus of research shifted to providing a more systematic account of the interface between these instruments than could be found in the existing literature. This book provides an updated and slightly expanded version of that original research project. Given its origins, primary thanks must go to my wonderful doctoral supervisor, Albertina Albors Llorens, for getting this project from proposal to PhD, to ultimate publication. Her advice, support and kindness during my three years of research was utterly invaluable. My examiners, Rosa Greaves and Angus Johnston, provided helpful feedback and much-appreciated encouragement to develop the original thesis into a monograph. The manuscript also benefitted from thoughtful comments from Bill Allan, plus useful criticisms and suggestions for improvement from three anonymous referees. Peter Dunne provided eagle-eyed editing skills at the doctoral stage, while the editorial team at Cambridge University Press has been fabulous in bringing my initial proposal to polished reality. I am grateful for support of a more material kind from the UK’s Arts & Humanities Research Council and the Competition Authority of Ireland. (My interest in the relationship between competition law and regulation is perhaps more understandable given my past life in competition enforcement in a small Member State.) Corpus Christi College,