In the theoretical part of the doctoral dissertation; there is determined peculiarity and development of the international markets and business in general. There are also determined theoretical elements of international marketing, as well as the importance of development of international markets and marketing development for Croatian business. Expanding on the international market can help to reduce the dependence of the Croatian business subjects on the domestic market, enable the dispersion of risk from business activities on multiple markets, enable the acquisition of international experience and knowledge, acquisition of experience for development of other forms of conducting business as many other types of benefits. Therefore it was necessary to determine the stage of development and the possibilities of the Croatian business subjects to accomplish competitiveness on international markets. The theoretical foundations for reaching this goal brings to focus the development of knowledge in marketing and recognizing the key of macro and micro factors which influence the success of doing business on the international market. In the empirical part of the dissertation; a research has been conducted with the goal to determine the key factors from the marketing environment which have the most impact on the success of Croatian business subjects on the international market. In the data‘s, there are descriptive methods and inferential statistics that are being used. Depending on the research questions and hypothesis; there are different methods that are used; invariant, bivariate and multivariate statistical analysis that are identified as a crucial factor in this analysis that consists of 165 foreign and Croatian businesses. Based on the results of the empirical research; there is created an interrelated model of crucial factors for success on the international markets; as well as the scientific based suggestions and restraints for the further development of Republic of Croatia as a goal of achieving further business developments on the international markets.