This thesis constitutes the first comparative study of the phenomenon of alternative art galleries functioning during the 1970s in two neighbouring state socialist regimes, namely, the German Democratic Republic and the People's Republic of Poland. Firmly contextualised in the cultural-political climate of Honecker's and Gierek's quasi-liberalisation, it examines the socio-cultural function of non-conformist exhibition spaces and focuses, specifically, on two case studies: Galerie Arkade in East Berlin and Galeria/Repassage in Warsaw. By looking at a wide variety of practices produced in those spaces, this thesis investigates the commonalities and differences in how the galleries operated and how they related to the divergent post-Stalinist conditions. For instance, due to more repressive cultural-politics in the GDR, it proved more difficult to accommodate experimental practices in Arkade, since even exhibiting abstract art was problematic for the East German officials. Conversely, in Poland Gierek's liberalisation resulted in the state's limited acceptance of radical artistic practices such as performance and conceptual art but only in the marginal spaces of artist-run galleries. Despite their alternative status, the galleries were, to a certain degree, dependent administratively and financially on these socialist institutions and were at the same time exposed to surveillance by the state security services. These aspects of galleries' activities are often neglected and so to remedy this lack this thesis offers new perspectives on and insights into various aspects of the functioning of alternative culture in this region. The originality of this research lies also in its references to new archival material which has not been published, nor interpreted before. The interpretation of these rich primary sources makes use of a new theoretical framework that combines Michel Foucault's theory of heterotopia in a macro-level analysis and Henri Lefebvre's ideas on the social production of space in a micro-level analysis. In particular, the galleries' histories are seen in this thesis as intertwined with the advancing process of disintegration of state socialism in the Eastern Bloc as this was perceptible to varying degree in different socialist states. Accordingly, it argues that the galleries were symptomatic of and, simultaneously, contributed through various practices to the 'post-socialist condition'.