As for most international organizations, the Central American Integration System (CAIS) has been and is still facing a heavy legitimacy crisis. The Central American case goes deeper than the European “democratic deficit” highlighted by Moravcsik (1991). In fact, the proper existence of CAIS is regularly questioned because of a low effectiveness in terms of regional social development. Notwithstanding, CAIS is one of the oldest regional regime (1951) that recently develops regional public policies in a substantial way, particularly with the help of European and non European donors. Even if, the system is promoting its third wave of institutional reform, it is still suffering from a deep legitimacy crisis, especially in front of public opinion and non state actors. As a matter of fact, CAIS had to deal with this legitimacy challenge. As proposed in this panel, our paper will mainly focus on how CAIS faced this legitimacy challenge through a massive process of institutional change (Thelen, Mahoney, 2010) giving birth to a regional system of governance focused on democratic legitimacy (Rosanvallon, 2009). Moreover, we will empirically assume the original top-down process of legitimation through the study of “regional political elites”, more precisely the CAIS officials. Indeed, our main hypothesis lies in the fact that the paramount institutional changes (regional governance system, mechanisms of democratic legitimacy) have been promoted by actors that progressively gained their autonomy from Central American States, what precisely refers to A “self-legitimation” process. We will present the strategies through which these officials have been able to promote changes in order to foster legitimacy. We will also describe the complex frame of interactions that has been settled in this regional organization under scrutiny. Our analysis will be based on an institutionalist perspective (Fligstein, Sweet, Sanholtz 2001, Surel and Lequesne 2004). Furthermore, in the line of recent theoretical and empirical researches on regional integration sociology (Woll and Jacquot 2004, Favell 2008, Favel and Guiraudon 2008, Saurruger 2009) we will present the main results of our last field research (enquiry and semi-direct interviews) made in El Salvador (San Salvador) where stands CAIS headquarter.