Próleg i epíleg també en castellà ; The thesis The form of living in modern Belgian architecture" is a travel through the most industrialized cities of Belgium. lts main objective is to investigate the history of the social habitat in this country, with the aim to reveal the essence of the Belgian modernity and its compromise with the architecture and town planning. Through an excursus on the social housing development, from the nineteenth century to the garden-city,the investigation proposes an historical reconstruction of the modern social housing with a particular emphasis on the importance, growth and tate of neighbourhoods with high-density population. In fact, the hypothesis of this work is that the collective housing has been the innovative element in the experience of a new method of urban planning, and thus a generator cell of Belgian modernity. The research bases itself on the analysis of two projects of workers-city, Grand Hornu and Bois du Luc, built in the nineteenth century using architectural quotations and allusions to try to shape a new reality: the monad life-work. From this time onwards, the social architecture in Belgium was the protagonist of a major evolution concerning the birth of metropolis. Starting from the late nineteenth century, Belgian hygienists gathered the attention around the problem of living in an healthy city, and the need to offer to the workers, most of whom were employed in the many coal mines of the country, a dignified housing. At this time, the garden-city was becoming the most diffused spatial conformation supporting the belief that living in a natural environment could have restored the purity subtracted from the poisons of the devourer city. The new garden-city acted as an organism to encourage the construction of new housing and to propose solutions that consecrated the desire to give to the city a modern future, which could have been an example to export . Without doubts, the rising of architectural and urban theories urged the Belgian society to take care of the issues concerning new lifestyles and therefore experiment novel models of community with the aim to renew the society itself. In the early twentieth century, the enthusiasm of young architects animated Victor Bourgeois (1897-1962) , Huib Hoste (1881-1957), Louis Van der Swaelmen (1883-1929) and Anto ine Pompe (1873-1980) to be active in the debate forwarded by the CIAM, which resulted in the division into two main architectural trends pursuing either the line or the organic form. Later on, the debate on social housing became the cradle for chimeric suggestions, like the one presented in the thirties by the architect Juliaan Schillemans (1906-1943) ,who designed an ideal "world-city ", for thirty-five millions inhabitants, with the aim to redefine the style lifestyle of a society without boundaries. More pragmatically, in the 50s, architects groups like EGAU (Etudes en groupe d'architecture et d'urbanisme), formed by Charles Carlier (1916-1993), Hyacinthe Lhoest (1913 to 1983) and Jules Mozin (1914- 1995) and the Groupe L'Equerre (1935) raised, through a fervent political activism, a reflection on the topic of housing and how to redesign new spaces. In particular, L'Equerre collaborated with the Flemish architect Renaat Braem (1910-2001) who considered architecture as the art to reorganize the human, environment and an instrument to free the society from the hierarchies inherited from the past. On the other side, the works of Groupe EGAU and the architect Willy Van Der Meeren (1923-2002) distinguished themselves in the same current for a strenuous research in the low cost housing field and for the housing solutions presented in the competition organized by CECA (European Coal and Steel Community).