The paper shows how business clusters promote cooperation among companies and how they contribute to the competitiveness and internationalization of enterprises. The authors prove that a business cluster improves the competitiveness of member companies primarily by adding to their competitive potential and boosting their competition strategies. At the same time, the cluster has only an indirect effect on the competitive position of these businesses, the authors say. The relationship between competitiveness and internationalization is unclear. It is difficult to determine on the basis of available data if greater competitiveness resulting from a company's participation in a business cluster leads to this company's greater involvement in international business. It may well be, the authors say, that the relationship goes the other way: greater internationalization leads to increased competitiveness.