Résumé : Recent work on psychological entitativity has suggested that perceiving Europe as an homogeneous entity may increase identification with this group. We suggest that this effect might in fact be due to the positively valued political projects that these descriptions serve rather than to their intrinsic qualities. In line with this view, it was predicted that a positive relation between perception of similarity among European nations and European identification would be obtained only when similarity was presented as desirable for the accomplishment of the European integration project. Generally pro-European students in three Brussels secondary schools (N=122) read a speech stressing the efficiency of a policy - increasing similarities vs. preserving differences between countries - in the successful development of the EU, or no text in the Control condition. They then reported their level of European identification and their perception of similarity among European nations. Results show that countries were judged as less similar in the "Difference desirable" condition than in the "Similarity desirable" or control conditions (no text), while European identification remained stable. Moreover, Perception of Similarity significantly predicted European Identification only when similarity had been presented as desirable. In the two other conditions - when no text was presented and when difference was presented as desirable -, there was no significant relation between these two variables. This study shows that perceiving an in-group as a homogeneous entity does not enhance identification unless it is considered as desirable for the in-group. In the case of the European Union, it suggests that perceiving heterogeneity among countries should not impede the development of a European identity.