The European Union has come a long way since the Second World War. Through an economic union and the European internal market, EU Member States have been able to grow and flourish. While it is clear that the intra-EU trade is likely to be of high importance for EU countries, given the advantages of the European internal market, the role of extra-EU trade in the development of the EU remains more of a mystery. With a hypothesis that assumes extra-EU trade is crucial for EU development, this thesis analyzes the development of the EU, along with the developments of intra-EU and extra-EU trade. Through correlation and regression analyses, the relation between extra-EU trade and the development of the EU has been assessed. In addition, the effect of the EU status on the development of countries has also been assessed, to determine how important being part of the EU is for the development of a country. Before analyzing these relations, however, the term “development” has been defined in context of the development of countries and economic unions. Subsequently, an analysis has been carried out to determine which measurement method to measure development is the best and most efficient one to use for this research. This resulted in the usage of the Human Development Index (HDI) as a means of measuring development. With the required data collected, the correlation and regression analyses are carried out, and both the extra-EU trade and the EU status of a country moderately positively affect the HDI and thus the development. However, while the extra-EU trade appears to support development and play an important role, it cannot be considered crucial for EU development. Therefore, the conclusion is that the hypothesis is not rejected, but can also not be fully accepted.