ENThe paper is a study of house-building cooperatives in the Lithuanian SSR as a field of architectural experimentation in planning, design and construction of mass housing during the late Soviet period (1960s–1980s). The house-building co-operatives were re-introduced in the USSR in 1962 as a substitute for the cessation of private single-family houses in large cities. Politically and economically, house-building co-operatives were seen as a solution to the difficult situation posed by the well-known Soviet apartment shortage because co-operative apartment arrangements meant that residents contributed their own funds to the process of building their homes, thereby avoiding the waiting list. The important change that housing co-operatives offered was the possibility for better-to-do citizens to obtain housing luxuries that were previously available only to the privileged party nomenclatura. From an urban planning perspective such a concentration of previously single houses into multi-apartment buildings was meant to minimise the municipal land taken up for housing and reduce the cost of engineering infrastructure. At the same time the introduction of co-operative housing resulted in more varied residential building designs (including more comfortable apartment layouts and better selection of materials), engaging in the process departments of experimental design at the State Design Institutes. In this paper a hypothesis is proposed that the development of co-operative housing stimulated architectural experimentation for groups concerning both privileged residents (because the process of co-operative housing accelerated the concentration of more affluent urban dwellers) and architects, who wished to express more varied residential planning ideas. [From the publication]