After successive waves of EU enlargement, and pursuant to the entry into force of the Lisbon Treaty, the European Court of Justice finds itself on the brink of a new era. Both the institution itself and the broader setting within which it operates have become more heterogeneous than ever before. The issues now arriving on its docket are also often of great complexity, covering an unprecedented number of fields. The aims of this volume are to study the impact of these developments, examine the legitimacy of the Court's output in this novel context and provide an appraisal of its overall performance. In doing so, specific attention is paid to its most recent case law on four topics: the general principles of EU law, external relations, the internal market and Union citizenship.