Building heating, ventilation, and air conditioning (HVAC) accounted for 14.0% of primary energy consumption in the United States in 2013, or 13.6 quadrillion British thermal units (“quads”) per year. In addition to the season and weather in various U.S. regions, this consumption is determined by the heating and cooling facilities in the buildings, by the thermostat settings and other choices of building managers and occupants, and finally by the building envelopes. Windows are essential and costly elements of building envelopes, and the heat that flows out through windows in cold weather across the U.S. consumes about 3.9 quads of primary energy. The ARPA-E Single-pane Highly Insulating Efficient Lucid Designs (SHIELD) program seeks to reduce this consumption by funding the development of energy-efficient and cost-effective retrofits for the substantial remaining stock of single-pane windows in the U.S. ARPA-E analysis indicates that a fully successful single-pane retrofit campaign will reduce total building energy consumption by 1.2 quads, or 1.3% of domestic energy use. As envisioned in this SHIELD program, it will also address the water condensation and occupant discomfort that are associated with single-pane windows in cool climates.