The subject of this thesis is dual citizenship in the Republic of Croatia. Citizenship is defined as a special legal relationship between the state and the individual that involves their mutual rights and obligations. Through the process of globalization and the weakening of the nation-state, the relationship between the state, citizens and foreigners has changed, and the number of individuals with dual citizenship has increased. The main law that regulates the issue of acquiring and terminating Croatian citizenship and that expresses the legislator's attitude towards dual citizenship is Croatian Nationality Law. Dual citizenship can refer to a case in which two states consider an individual to be their citizen, and a case in which an individual, in addition to the citizenship of a certain state, also has citizenship at a higher level. An example of the latter is the citizenship of the European Union, which was automatically acquired by all its citizens upon the accession of the Republic of Croatia to the European Union. In four parts of the paper, we presented all aspects of the issue of dual citizenship in Croatia. The first part defines the concept of dual citizenship, its origin and termination, with special emphasis on the cross-border type of dual citizenship. The second part presents the change in citizenship policy in the Croatian legal framework since gaining independence. The third part discusses citizenship of the European Union and its relationship with the citizenships of the member states. The fourth part discusses the responses of Croatia and Bosnia and Herzegovina to the challenges that arise in practice due to their common citizens.