This book introduces the concept of responsibility to the field of EU citizenship law by making three significant contributions to the field.Firstly, it examines the responsibility of all four protagonists in EU citizenship law (the individual, the home and host Member States, and the Union itself), providing a more holistic understanding of EU citizenship. Secondly, it challenges a prevailing narrative that nationality plays a declining role, arguing instead that the continued significance of the home Member State reinforces rather than weakens the protections of EU citizenship. Finally, it presents individual EU citizens in a more nuanced light, highlighting both their rights and responsibilities. This approach provides a richer understanding, allowing for a meaningful assessment of EU citizenship as it stands at a crossroads.