This toolkit aims to assist practitioners in undertaking a standard upstream diagnosis to inform policies and programs in the housing sector at the city level in developing countries, with a focus on the supply side. It is designed to balance the need for achieving a comprehensive assessment of a complex sector like housing and the political impetus to identify problems and take actions within a short timeframe. It aids a team in evaluating a city’s housing challenges and developing a prioritized set of possible interventions – both reform and investment – that government and private entities can take to address them.