The relevance of the study is conditioned by the fact that since the end of the 1980s, as a result of the “Velvet Revolution”, the expansion of the European Union to the East has become an urgent task for the entire European continent. It has been a long time since the European Union entered a new stage of development, which is considered the most difficult in the history of European integration. Countries that got rid of the totalitarian regime expressed a desire to build a democratic society. However, states that had just gotten rid of communist sentiment did not meet any criteria that would allow them to be European Union members. The main purpose of this study is to investigate the transformation processes in such states of Central and Eastern Europe as the Republic of Bulgaria, the Republic of Poland, The Republic of Hungary, the Slovak and Czech Republics, and Ukraine. To determine how the process of European integration took place in the above-mentioned countries, to analyse the correlation between reforms and integration processes in these countries, and to consider the consequences of the introduction of European norms on socio-economic development. The following scientific methods were used when preparing the paper: structural and functional, dialectical, logical analysis, synthesis, comparative analysis, analysis of scientific literature, and generalisation. The main result is theoretical and practical changes in the Central and Eastern Europe countries during transformations and European integration processes, analysis of the political theory of European integration and its main provisions, which are still being discussed in scientific communities. The study also aims to investigate problematic issues of integration processes that require a comprehensive analysis. This study is of particular importance from the standpoint of practice, since a comprehensive analysis of the problems that arise during European integration processes in the future would allow avoiding them, which is positive for both European Union members and candidate countries. In the course of the study, statistical data, scientific investigations, political and scientific sources were analysed, and practice in these republics was considered. At this stage, the topic of transformation processes in post-socialist countries during the process of European integration requires special attention and more detailed analysis