The growth in world population and in demand for energy worldwide, in particular in developing countries, is highlighted. The reflection on CO2 and other greenhouse gas emissions, and the subsequent effects on the shape of climatic changes, are examined. The paper then assesses the energy intensity of economies from different parts of the world, rich and poor, and demonstrates that significant savings in energy consumption can be made. Finally, the scope and means of achieving the expected improvements in energy efficiency in the different sectors of the economy (commercial and residential, industry and transportation) are discussed in detail. Examples of the energy saving technologies are presented.