Cidade de Deus serves as the inspiration and case study for this publication, a widely relevant investigation into the gradual appropriation and customization of standardized mass housing. Rio de Janeiro’s once notorious favela, which grew out of a government housing program, is today a safe and vibrant neighborhood, not to mention a viable counter-model to gated real estate development. This research-based design study from the ETH Zurich unpacks the implications of the hybrid environment of Cidade de Deus as it exists today. What results is a globally applicable model for improving mass housing programs using the ingenuity and resourcefulness of informal practices.