Civil society is often presented as one of the decisive forces which contributed to the fall of the communist regime. Both history and collective memory have preserved the symbolic meaning and the actual political power of the social movement organized within the frames of the trade union Solidarnosc . The socio-historical analysis of associational life in Poland, which we propose in this thesis, and in particular the analysis of the present situation, show that associational life in general is still more influenced by the communist past than by the new context of democracy. In contrast to this observation it can be argued that as the communists gained power a large change was occurring within the sphere of associational life. This change was so radical that presently there is no palpable link between contemporary organizations and those existing before 1952. Such inertia of organizational patterns of associational life is even more surprising if compared with the spheres of economy and politics which both seem profoundly transformed after the fall of the communist regime. This fact leads us to ask what is the actual role of organizations of civil society (former communist mass organizations, organizations affiliated to the Catholic Church, groups linked to former democratic opposition, and organizations dissolved by the communists and revitalized after 1989) in the process of transition of a postcommunist society.Our socio-historical study is a starting point for a more general theoretical reflection. We propose an ideal-typical definition of what we call a Civil Society Organization (CSO). This definition is intended to provide a common point of reference for two major theoretical traditions, that of civil society, and of the third sector. Moreover, such a definition permits us to avoid the usage of the more superficial terms such as non-governmental organization or nonprofit organization. Both these terms were employed in diverse contexts and are strongly influenced by political and economic discourses. Last but not least, our analysis of Polish associational life helps us to be more precise with certain aspects of our definition, notably the ethnic and religious dimensions of a CSO.