The question of whether Intergovernmental Organizations (IGOs) have a socialization effect on member state preferences is central to International Relations. However, empirical studies have struggled to separate the socializing effects of IGOs on preferences from the incentives generated by IGOs that may lead to foreign policy alignment without altering preferences. This paper addresses this shortcoming. We adopt a new approach to measuring state preferences by applying text analytic methods to country statements in the annual UN General Debate (UNGD). The absence of inter-state coordination with UNGD statements makes them ideal for testing socialization effects on state preferences. We focus on the European Union (EU), enabling us to incorporate the pre-accession period – when states have the strongest incentives for foreign policy alignment – into our analysis. The results of our statistical analysis demonstrates that EU membership has a strong socialization effect that produces member state preference convergence, controlling for incentive effects.