Piet Jan Slot is one of a notable group of innovators who have greatly elucidated the role of law in the construction of European integration. His retirement this year from the Law Faculty at Leiden University has occasioned this festschrift, in which forty-six colleagues, past and present, recognize his many sterling contributions and engage with issues central to his work. Many of them focus on aspects of European competition law, while others extend his preoccupations with such fields as environmental regulation, energy, transport, and the interfaces of European law with both Member State law and international (global) law. Ranging from historical tendencies to emerging trends and possibilities, the authors explore dozens of relevant topics, including the following: harmonization of EU law; progress of the concept of technical barriers; economic justifications and the fundamental freedoms; the Keck dichotomy between product requirements and selling arrangements; private antitrust enforcement in an international context; retail price maintenance; competitors role in the public enforcement of the state aid regime; scope of judicial review of sanctions in competition law; competition and security of supply; ownership unbundling; proliferation of EU regulatory agencies; and the influence of the ECJ on the interpretation of the ECHR. Conscious of Slot's ability to identify and analyse the crucial issues of a complicated matter and express them in a clear way adequately attuned to the listener, the authors tackle some of the most complex areas in European law. Although, like Slot, they consider European integration as a value that should be respected and fostered, by no means do they uncritically accept European law or the way it is made. They carry on Slot's work in interpreting and applying European law to search for solutions that maintain, develop and enrich the legal order established by the various European Treaties. This challenging and absorbing book offers everyone interested a rich selection of topical as well as controversial issues in a number of areas of European law. It is a fitting tribute to the diversity and reach of Slot's contribution to these fields as an academic and practitioner over a period of some forty years.