Given the increased importance of retailing in distribution channels, or in the whole economic system, it is necessary to continue the study of theories that explain the changes and development of forms of retail business units. In this sense especially important are new theories: "combined theory" and "theory of advantages based on resources". These concepts are especially important for explaining the process of expansion of certain forms of retail business units by the world's large retail chains from one to other countries. The paper highlights reasons of still growing importance of retailing in the n ational economy (given the proposals for new indicators). Besides being the highlight of so far the best known concepts of explaining the change in the form of retail business units, paper also highlights the basic indications for the creation of new concepts: further development of trade function in terms of their concentration and increase of market transparency. Contemporary changes are caused by factors that lead to internationalization and globalization processes in the global economy. Hypothesis could be verified by the finding of certain tendencies and regularities in their movements and their relations. However, the paper gives only some indications of concentration trends in the Croatian retail trade and the development of e-retailing, and some comparisons with the development of international retail chains.