In this article, citizenship and its notion, legal nature and historical comparative-legal analysis are presented. All the Conventions, adopted globally by the United Nations or regionally by the Council of Europe, American Convention or Organization of African Unity, underline the significance of the citizenship on the international level, in exercising human rights and freedom, aiming at lowering the number of persons without citizenship. At the beginning, citizenship was regulated by the norms within civil code, and then by the special laws, while in some states the citizenship is regulated by the constitutional norms. Every state is sovereign when deciding on the choice of the basic principles of the acquisition of citizenship and in most cases it combines them. According to the principle of the origin, children follow the citizenship of their parents regardless of the place they were born. According to the principle of the birth place, parents ' citizenship is not of relevance, but the birth place, e.g. children acquire citizenship of the state in which they were born. Unlike first two principles, used to establish the citizenship for the children at the moment of their birth, the permanent residence is used for the establishment of the citizenship of the adult persons willing to acquire the citizenship. This principle is almost nowhere the basic one and it is mostly combined with two others. Which one will prevail as the basic one depends on the standing position of the law maker, based on the national interests. It is almost impossible to apply only one principle, but the combination of a few, mostly the origin (Ius sanguinis) and birth place (Ius soli). The marriage is of relevance for the citizenship status of married persons, which is important for facilitated acquisition of citizenship, when other conditions are fulfilled, and it can be relevant for the termination of citizenship. In the previous laws on citizenship, affiliation to the local community or homeland influenced the process of acquisition of citizenship. Actual legal systems do not recognize the affiliation to a homeland. In practice, due to implementation of different principles of citizenship acquisition, there are some cases of stateless persons (persons without citizenship), as well as persons with two or more citizenships. In the legal procedures of acquisition and termination of citizenship, almost every state takes a decision based on the discretion. The paper focuses on the acquisition and termination of citizenship in the Republic of Serbia. The basic principle of acquisition of Serbian citizenship is the origin, but it is combined with the principle of the birth place, as well as with the principle of permanent residence in cases of naturalization of foreigners with permanent residence in the Republic of Serbia. The Ministry of the Interior is the competent institution to decide on both the acquisition and termination of citizenship, after having examined whether all legally binding conditions were fulfilled, but the decision could be made at the discretion of the relevant authority. The administrative court, controlling all the decisions on requests for acquisition or termination of citizenship, may decide on legality of the administrative act, but cannot interfere with the essence of the decision.