Urban density is central to pressing questions concerning low-carbon lifestyles, affordable housing and global land use patterns. However, for many densifying cities, problems of inequality, climate emissions and social sustainability often remain unsolved or exaggerated. Adopting a relational perspective, this paper explores the politics of urban densification in Oslo, Norway. Arguing that urban density is assembled as particular political projects, the paper seeks to understand the achievements urban densification projects bring together, from housing policy to environmental policy, property schemes and financial strategies. Based on a qualitative study of urban densification strategies and projects in Oslo, the paper develops a typology of hegemonic and counterhegemonic urban density discourses and contributes to a discussion of how economically, socially and environmentally different kinds of urban densities may be assembled.