This doctoral dissertation deals with the constituting i.e. formation of the function of the President of the Republic in former socialist countries. It analyses in greater detail the constitutional role of the President of the Republic of Estonia, Latvia, Lithuania, Poland, Czech Republic, Slovakia, Slovenia, Croatia, Hungary, Romania and Bulgaria, i.e. eleven Member States of the European Union. These states put in place the office of President of the Republic as the individual Head of State in the 1990s. In the process of the formation of the function of the President of the Republic, the countries analysed took inspiration from other established legal systems. In this context, while taking into account their own historical, cultural and political reasons, these states have experienced a spill-over of individual constitutional institutions leading to the creation of a sui generis institutional equilibrium i.e. separation of powers, or lack thereof, which has a decisive impact on the relations between the Government, the Parliament and the President of the Republic, as well as, consequently, on the functioning of the authority of the state itself. Some political systems initially showed a tendency to introduce a system with a stronger head of state, inspired by presidential or semi-presidential republics, but the majority of these countries gradually limited the powers of the President through the constitutional development and stabilisation of their political space. The situation is, however, different in those countries where, from the very beginning of the formation of the function of the President of the Republic, the constitutional legislator conferred upon the President mainly representative powers, following the example of systems with parliamentary supremacy, thus preventing the President, in accordance with his or her neutral role, from being able to adequately address ‘crisis situations’ in relation to the blocking of authorities arising from conflicts between the Parliament and Government. Hence, the analysed constitutional regimes have now seen certain elements appear which are “alien” to different political systems and which determine the (specific) position of the Head of State. The position of the President of the Republic, and in particular the extent of his or her powers and the resulting relationship with the legislative and executive bodies, is also one of the fundamental criteria of the classic classification of political systems. In addition to the powers exercised (mainly in the legislative and executive domains), the President’s position is also influenced by the way he or she is elected. Compared to traditional western systems, the way in which the President of the Republic is elected in most of the former socialist states in question is not directly correlated to the extent of his or her formally defined powers. Based on the analysis of comparative law carried out, it can be concluded that in a regime like the one set up in Slovenia (where the constitutional legislator strengthened the President’s legitimacy by holding direct elections, but at the same time conferred upon him or her weak, mainly representative powers), the President’s position is the weakest among the eleven former socialist states analysed.