This “open file” research report from Applied Technology Building Group was written to provide a comprehensive review of climate science, climate policy, the status of US energy use and greenhouse gas (GHG) emissions, and the decarbonization of US buildings. The report discusses the importance of a “total carbon” approach when setting policy or making decisions related to insulation materials, which deliver substantial benefits for energy efficiency and the avoidance of building operational GHG emissions. It also explores the importance of building insulation to enable the energy demand reductions needed to decarbonize new and existing buildings.