The introduction presents the book’s main claim, namely that citizens have a moral right to democratically decide by which criteria they grant migrants citizenship as well as to control access to their territory in the first place. This means that they can permissibly exclude outsiders who would like to join or to enter. Moreover, while there are some limitations of the scope of the right, it is nonetheless far-reaching and robust, and there are no limits on the reasons for exclusion. The section will also briefly describe and explain and thus assure the reader of the accessibility of the main types of normative arguments used throughout the book. It then gives an overview of the structure of the book and the topics to be covered.