Résumé : Small states’ scholarship is characterized by extreme conceptual and definitional richness, yet it is fundamentally fragmented. What hinders the possibility of finding clear-cut lines on what constitutes smallness, and its implications on states’ behaviours, are different understandings of power. Studying small Member States in the European Union is fraught with even more difficulties due to its peculiar political and institutional construction and the formal and informal norms of its policymaking. Absolute and relative definitions of smallness and power result inaccurate explanatory variables, not able to grasp the consensus-oriented and friendly environment which is the EU for small Member States.The aim of this thesis is to challenge these traditional approaches by showing how an account based on the Social Identity Theory can bring about a synthesis of the definition-debate and provide a thicker understanding of what constitutes a small state and the determination of its foreign policy behaviour. At the same time, it contributes to the literature by investigating how smallness affects the participation and role of Member States in the European Neighbourhood Policy.Focusing on the case study of Estonia and the Eastern Partnership initiative and relying on a triangulation of semi-structured interviews and document analysis made possible to test a SIT approach and make three kind of observations. First, smallness can be understood as the psychological size of being a status-seeker and not counting on sufficient material resources that could be translated on a value dimension in the capacity to grant status to others. Second, smallness has spill-over effects on states’ foreign policy behaviour. In particular, small Member States research of status affects their participation in the European Neighbourhood Policy by making them adopt social creative strategies which are based on a mix of commitment, immaterial resources, smart administrative capabilities and institutional knowledge. Third, the embracement of these behaviours has the purpose of overcoming actual smallness by finding a new value dimension through which small states can gain international attention and prove to be reliable partners. This eventually enhance their intra-EU role and status.