The purpose of this article is to define the phenomenon of regionalism from the sociological perspective. Regionalism as such appeared in Europe around the mid-nineteenth century, and since then has become an object of scientific research. The article proposes an integral definition of regionalism and describes its four dimensions: identity, institutions, ideology and practice. It also identifies the cultural, economic and political types of regionalism and outlines the process of shaping regionalism in the long-term perspective. The article describes the influence of the nation state on the evolution of regionalism and analyses the relationship between regionalism and processes of state decentralisation. It also describes mutual relations of the European Union and its policies with regionalism, which is being transformed due to globalisation.