Population and societal growth coupled with technological progress, have all lead to a rapid increase in energy usage and consequent depletion of fossil fuel reserves. Although one could question the credibility of these estimations as supported by the recent revision in the case of natural gas reserves, the fact that the worldwide demand will keep on growing unabated leaves no doubt that the solution is not to procrastinate but to look for alternative sources of energy. At the same time, there is a growing belief that the use of fossil fuel and the consequent release of greenhouse gases are mainly responsible for the observed global warming trend. Hence there is a big push for developing new sources of clean, alternative energy for replacing the fossil fuels. In addition, if the source is renewable, that will further help provide a long term solution. However, one should note that the Sun is the main source of energy; the energy received from the Sun is transformed into various sources like solar, wind, ocean, geothermal, nuclear, biomass, fossil fuel, etc., over widely differing space and time scales by mainly ecological and artificial processes. The term renewable has a spatial and temporal connotation. Hence what is “renewable” for one nation or part of the world may not be renewable and in fact even be available for another part of the world. Thus energy source has become an important commodity for survival and progress and has to be evaluated on thermoeconomic and socioeconomic bases. It requires 21st century cutting edge science, technology and systems for harvesting energy from the available sources and transforming it efficiently and economically into electricity, heat or power required for human consumption with minimal perturbation to the ecology. It is also important to note that the present energy crisis has occurred mainly because of dependence on only a few sources. Hence this needs to be addressed not only by exploring and evaluating all possible sources but also by developing systems for efficient transformation, storage and distribution of energy. All this involves development of technology in all areas and their cross transplantation for reaching the goal and sustaining the progress.