Buildings are responsible for about 40-quadrillion BTUs of the total energy, i.e., ~ 40% of the energy supply, of the United States. Improvements in the energy efficiency of buildings have significant impacts on the overall energy consumption and the battle against global warming. This volume of the Annual Review Of Heat Transfer (ARHT) covers some recent advances and opportunities related to the energy efficiency of buildings. Topics covered include building energy modeling (chapter 1), vacuum thermal insulation for building envelopes (chapter 2), window technologies (chapter 3), building thermal energy storage (chapter 4), heating, ventilation and air-conditioning (HVACs) (chapter 5), personal thermal comfort and regulation (chapter 6), and cooking technologies (chapter 7). ARHT, Volume 21 is an excellent resource for researchers interested in building energy savings.