This paper is the output of an exercise that aims to build the foundation for future work by the Cities Climate Finance Leadership Alliance (the Alliance) through a structured approach to analyze the challenges and priorities relevant to cities in decarbonizing the buildings sector. It is not an exhaustive study of zero carbon buildings, but rather a guide for future alliance work and exercise to build in-house knowledge. Buildings contribute 37% of global energy-related CO2 emissions. Nine percent of emissions are from on-site energy generation, 18% are from grid electricity, and 10% are from materials and construction.