After a first career as Professor of Physics, University of California at Berkeley, working in experimental particle physics at Lawrence Berkeley National Laboratory (LBNL), I was prompted by the 1973 Organization of Petroleum Exporting Countries (OPEC) oil embargo to switch to improving energy end-use efficiency, particularly in buildings. I cofounded and directed the Energy Efficient Buildings program at LBNL, which later became the Center for Building Science. At the Center we developed high-frequency solid-state ballasts for fluorescent lamps, low-emissivity and selective windows, and the DOE-2 computer program for the energy analysis and design of buildings. The ballasts in turn stimulated Philips lighting to produce compact fluorescent lamps. When they achieve their expected market share, energy savings from products started or developed at the Center for Building Sciences are projected to save American consumers $30 billion/year, net of the cost of the better buildings and products. In terms of pollution control, this is equivalent to displacing approximately 100 million cars. We did the analysis on which the California and later the U.S. appliance standards are based, and we also worked on indoor air quality and discovered how radon is sucked into homes. We worked closely with the California utilities to develop programs in "Demand Side Management" and "Integrated Utility Planning." I also worked in California and New England on utility "collaboratives" under which we changed their profit rules to favor investment in customer energy efficiency (and sharing the savings with the customer) over selling raw electricity. I cofounded a successful nonprofit, the American Council for an Energy-Efficient Economy, and a University of California research unit, the California Institute for Energy Efficiency, and I served on the steering Committee of Pacific Gas and Electric＇s ACT(2) project, in which we costeffectively cut the energy use of six sites by one half. Starting in 1994, my third career has been as Senior Advisor to the U.S. Department of Energy Assistant Secretary for Energy Efficiency and Renewable Energy.