This paper explains the concept of economic integration and investigates income convergence in the member states of the European Union, focusing on the period from 2000 to 2023. The topic of income convergence is important as it provides insights into how and why economic disparities decrease or increase over time. The main objective is to explain economic integration and explore beta and sigma convergence at the level of EU member states. Furthermore, the aim is to compare Croatia's convergence with other EU member states through relative transition curves. The research was conducted using data from Eurostat on Gross Domestic Product per capita (GDP per capita) expressed in purchasing power parity. The study applied beta and sigma convergence analyses and relative transition curves. Beta convergence was analyzed using the panel method with annual data and a fixed-effects model, while sigma convergence was represented through the coefficient of variation, which is the ratio of the standard deviation to the mean of the data. The results of the research on beta and sigma convergence align, and the combined findings indicate that convergence has been achieved in the EU27 countries, in OECD member states, and in the northern and southern EU countries, while in the EU-27 countries during the post-COVID-19 pandemic period, convergence has not been fully realized. Croatia's performance compared to other EU member states is depicted through relative transition curves, and the conclusion is that Croatia still lags behind the EU average, altrough GDP growth has been recorded since joining the EU.