Statelessness is a situation where an individual is not considered a national by any state. It is estimated that the global number of stateless persons currently exceeds 10 million, and although the majority of statelessness cases concern Asian countries, there are over 600,000 such individuals in the European Union. Albert Einstein (who renounced his German citizenship), Osama bin Laden (deprived of Saudi Arabian citizenship as a terrorist), and the character of Viktor Navorski, an Eastern European tourist played by Tom Hanks in the film "The Terminal" (whose country of origin formally ceased to exist during his journey to the USA, making him an airport resident), were all stateless. In addition to such individual, curiosity-arousing examples, mass statelessness, which is associated with serious human rights violations, can also be identified. Mass statelessness historically affected Jews deprived of citizenship by the Nazis and currently affects, for example, the Muslim Rohingya minority living in Burma, who are described as the most persecuted minority in the world. The above examples already demonstrate that statelessness pertains to highly diverse situations. This should be reflected in legal research on statelessness; however, there is currently no comprehensive study of these issues from the perspective of the specific characteristics of different "types" of stateless persons, in both historical and contemporary contexts. Analysis predominantly focuses on the sources of statelessness, which constitutes a different approach from the one proposed. For instance, regarding the category of "stateless children," several different sources of statelessness can be identified; however, distinguishing this category of stateless persons is justified by shared issues concerning instruments for reducing statelessness or matters related to protection. Statelessness became a subject of regulation in international law as early as the 1930s. After World War II, two conventions dedicated to stateless persons were adopted. Despite these regulations, statelessness has not been entirely eliminated, which some authors consider a "puzzle" of sorts. One of the problems is the lack of proper transposition of international regulations into national legal systems, as well as the lack of analysis of statelessness from the perspective of national law issues. In the proposed project, I will undertake an analysis of the significant problem of how stateless persons should be identified (how they differ, for example, from persons of undetermined nationality). In my research, emphasis will be placed on issues of national legal systems, with due consideration for international legal matters.