This paper investigates the effects of using the funds from the European Social Fund on certain labour market indicators in Croatia. These funds became available to Croatia by joining the European Union, so it can be indirectly talked about the impact of Croatia's accession to the European Union on labour market factors. The paper aims to quantify the effects of Croatia's accession to the European Union and the use of the European Social Fund on the Croatian labour market and investigate whether the changes are statistically significant. The paper analysed whether joining the European Union affected reducing the rate of long-term unemployment, increasing the rate of adult participation in education and whether there is a greater influence of the European Social Fund on long-term unemployment in less developed local self-government units compared to more developed local self-government units. The doctoral thesis consists of six chapters. The introductory chapter presents the research problem, objectives and three given hypotheses, and the expected scientific contribution. In the second chapter, the key terms of the labour market were defined, and an overview of the literature related to long-term unemployment, lifelong learning and adult education and the benefits of economic integration are presented. The third chapter describes the labour market in Croatia using basic indicators and a review of the literature related to the effects of the European Social Fund. Also, the implementation of the European Social Fund through the Operational Program Effective Human Resources 2014-2020 is described. The fourth chapter presents a descriptive analysis of the data and a description of the counterfactual analysis model (difference-in-differences and synthetic control methods) that will be used to prove the hypotheses. The fifth chapter contains an empirical data analysis in which the hypotheses of the thesis are tested. The last chapter presents the conclusions of the work. Three main hypotheses of the doctoral thesis are: • H1: The use of funds from the European Social Fund affected the reduction of long-term unemployment among the unemployed in the age group 40-64 in the Republic of Croatia • H2: The effect of using the funds from the European Social Fund on the employment of long-term unemployed persons in the age group of 40 and over in the Republic of Croatia is greater in less developed local self-government units • H3: The use of funds from the European Social Fund had a statistically significant effect on the growth of the participation rate of adults in formal and informal education Referencing to the results of the research, it can be concluded that Croatia's accession to the European Union and then the availability of ESF funds had positive effects on the labour market in terms of reducing the share of long-term unemployment, especially in less developed parts of the country, while the positive impact on adult education was absent.