On July 1, 2013, the Republic of Croatia became a full member of the European Union after intensive preparations and formal accession negotiations. This entire process included a series of legislative, institutional and many other adjustments, the consequences of which are already quite reflected in many spheres of Croatian society, but it can still be reasonably expected that the main (structural) effects of this process will be long term. Therefore, the motivation for more detailed research, analysis and comparison of current and past, as well as for judgments of the future effects of membership in the European Union, specifically on the competitiveness of Croatian tourism, was imposed. Accordingly, the competitiveness of tourism and the effects of membership in the European Union on the business and competitiveness of Croatian tourism, applying the methods of quantitative analysis, is a topic that is dealt with through a doctoral thesis, with the aim of expanding scientific and applied knowledge on the analysis of the country's competitiveness as a tourist destination, placing the above in the broader context of the European of the Union. Competitiveness is an extremely complex and multidimensional concept that cannot be considered unambiguously in terms of the key factors that can provide such an advantage to a company or state. In accordance with the set problem and the subject of the research, the basic scientific hypothesis of the doctoral thesis (H0) was formulated, which reads: The accession of a country to full membership of the European Union has a statistically significantly positive effect on the competitiveness and business of tourism in that country, and the main effects of these processes are long-term. Since the basic research hypothesis contains several relatively independent relations between different variables, auxiliary hypotheses were also formulated:PH-1: The improvement of macroeconomic conditions and competitiveness factors of the national economy has a statistically significant and long-term positive effect on the competitiveness of tourism.PH-2: Economic growth in the member states of the European Union has a stimulating effect on the business results of Croatian tourism and its competitiveness.PH-3: The increase in foreign investments and economic growth in the member states of the European Union have a statistically significant and positive impact on the operations and competitiveness of tourism in full member states. Based on the set problem, subject and hypotheses of the doctoral thesis, the basic goal of the research was defined: Systematically investigate the competitiveness of Croatian tourism in the context of European Union tourism by applying quantitative methods of analysis and comparison of the results of the tourism business of other European Union countries, and based on the obtained results, define recommendations for the future.