Assemblage thinking offers a new conceptual toolkit for analysing the relationship between society and space. However, major questions remain regarding both its ontological propositions and how it might be applied to the analysis of specific socio-spatial objects. This article contributes to these debates by using assemblage thinking to trace the long-term development of Rio de Janeiro’s favelas. These territories have undergone a range of seemingly contradictory changes over recent decades. On one hand, expanded infrastructure and service provision and improved social outcomes have meant favelas have moved closer to, and in some cases surpassed, areas officially designated as “formal”. On the other, they continue to be heavily stigmatised, targeted by exceptional forms of governance, and subject to militarisation and abuse by police and non-state armed groups. Tracing these developments over time, I argue that the favela is best understood as an assemblage of heterogeneous, interacting elements that operate according to diverse logics. Despite continual pressures to deterritorialise, or break apart, a density of components and relations has ensured the continual reterritorialisation of the “favela” as a distinct object of perception and action over more than a century, with far reaching consequences for residents and the wider city.