One of the main reasons to why a membership in the European Union (EU) is so attractive for prospect countries are the free trade agreements the membership entails. The free trade agreements mean that the whole EU opens up as one big market, where tariffs and tolls are no longer an obstacle to trade for its members. Therefore, this thesis analyses whether EU membership actually yields a positive effect on member’s trade. The time series analysis is based on a three-country sample consisting of Poland, Romania, and Croatia during the time period from 2001 to 2018. By applying multiple and Chow’s breakpoint tests, and country-wise and a pooled cross-section analysis model, we examine if the accession to EU impacts each country’s trade volumes. The results indicate that becoming a member of the European Union does not necessarily have a significant effect on Poland’s, Romania’s, or Croatia’s trade even if it is positive.