I. Justification of punishment and EU law: Introductory remarks. - II. Offenders’ rehabilitation according to national law, international legal instruments and the limits of EU criminal competences. - II.A. Offenders’ rehabilitation and fundamental rights: Domestic legal orders and international law. - II.B. The root of the notion of offenders’ rehabilitation in EU law: The role of the Charter of Fundamental Rights. - II.C. The structural limits of the Union’s criminal system and the interplay with national legal orders. - III. EU substantive criminal law: Is there room for rehabilitation goals? - III.A. EU choices regarding criminalization and their rationale. - III.B. Harmonization of criminal penalties and its impact on enforcement and execution. - IV. EU procedural criminal law. - V. National criminal law and Union citizenship rights. - VI. Conclusions. One notion in bits and pieces?