This report explores the critical role buildings can play in meeting climate change ambitions, using a portfolio of clean energy solutions that exist today. It considers the investment needs and strategies to enable the buildings sector transition, and the multiple benefits that transformation would deliver, including improving the quality and affordability of energy services in buildings for billions of people. Importantly, it sets out what policy makers can do to overcome the economic and non-economic barriers to accelerate investment in low-carbon, energy-efficient solutions in the buildings sector. This ranges from traditional, yet highly effective policy tools to ambitious, innovative market-based approaches that can increase the speed and scale of investment for a sustainable buildings sector. This is the third report in a series. In 2017, the International Energy Agency (IEA) explored how a very ambitious and rapid energy transition to address climate change might look, in support of the German presidency of the G20. In 2018, the IEA provided further insights into the fundamentally important role of energy efficiency to achieve that energy transition.