This study by C40, Cities Alliance, IIED, SDI, UNHabitat and ICLEI explores how upgrading informal settlements can lead to multiple climate resilience, inclusive, and low carbon development benefits. The report presents a case study of a holistic intervention in Mukuru, Nairobi, analysing the benefits of ten specific upgrading actions and offering several key recommendations for international, national, local policymakers and NGOs for future upgrading initiatives in informal settlements in cities.