The increasing cost of energy produced from fossil fuels has further renewed the emphasis on issues such as energy efficiency, alternative fuels and so-called sustainable technologies. Nearly 60% of the world' energy, today, is wasted as heat. A prime example is the internal combustion engine - where almost 70% of the fuel's calorific value is lost as heat through the exhaust and radiator. Thermoelectric devices can convert this waste heat to much-needed electric power. Thermoelectrics is also relevant for solid-state, noise-free, CFC-free, refrigeration and air-conditioning. These applications have been limited in the past, mainly due to the efficiency of materials, low power density, as well as scalability. Using thin-film nanoscale materials, which allow unique physics such as thermal conductivity reduction without deterioration of electronic conduction, we have been able to achieve a significant improvement in materials performance (Nature 2001). The thin-film nature has enabled devices with high specific power (in Watts/cc) and cooling densities (in Watts/square cm); the former is attractive for portable power while the latter is highly relevant for high-perforamance electronics cooling. In addition to these applications, our long-term vision is to contribute to energy eficiency, by harnessing untapped heat sources. We will describe our early efforts in the applcation of this technology for automotive waste-heat recovery. We will also compare the advantges offered by thin-film thermoelectrics for solar-thermal-to-electric power versus convenional photovoltaics.