Christian Calliess is Professor for Public and European Law at Freie Universität Berlin, Germany. From 2015 until 2018 he was on leave in order to work as Legal Adviser to the European Political Strategy Center (EPSC), the In-House-Think-Tank of the President of the European Commission, and Head of the Institutional Team. Before 2015 he advised the German Parliament (Bundestag), also representing it before the German Constitutional Court and the Court of the EU, among others in the ESM- and OMT-Case. He co-edits a Commentary on European Law and has regularly published on matters of European, constitutional and environmental law.