Everybody knows that improving building energy efficiency is key to reducing emissions, though successfully achieving it is perhaps the single biggest obstacle to meeting global ambition on decarbonization. But lowering carbon intensity is now just one driver of improving building efficiency, as energy costs around the world have soared over the last 12 months, focusing consumers’ and policy makers’ attentions on reducing energy demand. What are the ongoing challenges to improving building efficiency? How can we overcome those challenges in time to meet global carbon reduction targets? Can the high energy price environment—as well as security of supply concerns—in Europe and elsewhere lift ambition to the required levels? What are the biggest obstacles to improving building efficiency at the necessary pace to meet climate objectives? Is it a matter of policy, implementation or technological innovation, and do they go hand in hand? What are the key differences geographically on housing stock, temperature etc., and will they require different approaches to resolve? In the battle between efficient heating systems—heat pumps versus hydrogen—can there be only one true winner? What are the infrastructure investment implications of either technology?