In this paper we analyze regionalism and regionalisation as fundamental concepts and the emportance of their implementation and application in Republic of Croatia and in the european states. We are writing about different phases of development of regionalism in different european states and also about their peculiarities and specifics. We are mentioning the importance of documents of the European Union which support and legislatively determine regional degree and prescribe tasks of the regional degree of government. We stress on the importance of regionalisation of Croatia republic and its phases throughout history, especially from the nineties until today. Special emphasis in the paper will be on the role of counties as a form of regional government and the main bearer of regionalization in the Republic of Croatia. Through the beginnings of Croatian regional self-government with the adoption of the first ZLPRS, through constitutional amendments in 2000 to the abolition of state administration offices in counties and the assignment of public affairs to counties. In addition to the above, it is important to note that criticisms of the existing territorial structure of the Republic of Croatia and proposals for the regionalization of Croatia are also discussed as a response to the aforementioned criticisms. Towards the end of the paper, the regionalization of neighboring Slovenia is discussed, which contains many specificities and has itself gone through many problems