In this work, we analyzed regionalism and regionalization as basic concepts, and the importance of their implementation and application in the Republic of Croatia and European countries. We also listed the stages of development of regionalism in different European countries and their peculiarities and specificities. As well as the stages of regionalization throughout history in the Republic of Croatia. Despite many criticisms and shortcomings, the Republic of Croatia is on a solid path towards its regionalization. The opinions of experts and the experiences of other countries must be taken into account, and not be guided by political ambitions. EU legal documents contribute to the implementation and harmonization of the regional level of government, especially in member states. The EU has an important role to play in encouraging the development of the middle level of government. Regionalization processes are different in many European countries due to their own characteristics (cultural, social, historical), but the idea is very similar in all of them, to strengthen the regional level of government through processes of democratization and subsidiarity. Neighboring Slovenia is particularly interesting, where strong polemics were held about a new territorial organization with an intermediate level of government. Although it has been a thorny road, efforts for its regionalization are visible today, just like Croatia. Regionalism and regionalization of Croatia is a complex and interesting ongoing process, imbued with real and sincere wishes, but also with political opportunities for their realization. Let's hope that in the future the Republic of Croatia will be known as a highly decentralized country with strong regions, and serve as an example of efficient management to other countries.