About 67% of primary energy for electricity generation or 25.8 quadrillion BTU (quads) per year were released as waste heat at power plants in the US, and about 75% of the electricity produced is consumed in the residential and commercial sectors, where additional 7 quads of natural gas are consumed for water heating and space heating. Combined heat and power (CHP) systems have the ability to produce electricity on-site while utilizing waste heat for heating requirements, enabling primary energy savings of ~5 quads and reduction of CO2 emissions by ~200 million metric tons per year. Energy consumption analysis shows that an optimal CHP size for US residences is ~1 kW (electricity). Techno-economic analysis indicates that high-efficiency (~35%-40%), long-life (~10 years), low-cost (<$3,000 per kW), and low emissions are key requirements for widespread deployment of CHP systems. Some key technologies including materials requirements will be discussed.