This report reviews the historical development of citizenship law and the current citizenship regime in the five Nordic countries. It also presents statistics on the acquisition and loss of citizenship in each country over the past 10-15 years, provides a comparative analysis of the divergent development of citizenship policies in the Nordic region in the 2000s, and offers some reflections and recommendations on the future of citizenship in the Nordic region. The report was commissioned by The Nordic Council of Ministers and the project has been headed by the Institute for Social Research (ISF), in cooperation with the Peace Research Institute Oslo (PRIO). We thank The Nordic Council of Ministers for the financial support and the Norwegian Ministry of Justice and Public Security for their administrative efforts. We also thank the Swedish Migration Agency, the Norwegian Directorate of Immigration, the Icelandic Ministry of Justice, the Icelandic Directorate of Immigration and the Finnish Immigration Service for providing statistics on the acquisition and loss of citizenship in the respective countries. Finally, we thank Liza Reisel, research director at ISF, for valuable comments on a previous version of the report, and Jon Haakon Hustad, librarian at ISF, for helpful assistance in conducting the literature review. The report is a joint effort. It was written by the head of the project and senior researcher at ISF, Arnfinn H. Midtbøen, in close collaboration with Simon Roland Birkvad at ISF and Marta Bivand Erdal at PRIO. Midtbøen was responsible for writing Chapters 1 and 6, Birkvad for Chapters 4 and 5, and Erdal for Chapter 2 as well as the section on extraterritorial citizenship in Chapter 4. Chapter 3 was written in collaboration between Midtbøen and Birkvad and the concluding chapter in collaboration between Midtbøen and Erdal.