Today, there is a strong understanding of the potential economic, security, and diplomatic gains for the U.S. and China associated with collaborating on clean energy and climate change. Yet despite the identification of energy efficiency as a clear priority for both countries, which is underpinned by bilateral agreements and broad efforts to date, little analysis has been conducted to understand how the two countries can leverage collective opportunities and common intervention points to reduce building energy use. Two recently completed detailed studies completed by the authors for the U.S. and China identified possible pathways for drastically reducing energy use and carbon dioxide emissions by 2050. Informed by the identified solutions, this paper outlines collaboration opportunities that support each country to realize the vision. The opportunity assessment takes into account political context, country development status, building energy consumption and stock characteristics (such as age, growth, and turnover), impactful design and technology solutions, building sector reduction potential, and cost effectiveness. The ensuing collaboration assessment, based on these key considerations, identifies the best opportunities for the two countries to capitalize on each other's advantageous position to address shared challenges and yield mutual benefits.