Book excerpt: Energy appears to be a fundamental driving force of economic and political strategies as well as planetary stability. Energy-related issues such as (1) the availability of new energy sources and viable technologies, (2) the disparity in access to energy sources, (3) the role of energy in our societies (energy societal metabolism), (4) the energy support to the life of our cities (where about half of world population is going to live very soon), and (5) the energy demand for food security all over the world, are “hot” problems that humans will have to face within the framework of sustainability (ecologically sound production and consumption patterns associated with socially acce- able life styles), in terms of policies, technological development and economic processes. A coherent energy strategy is required, addressing both energy supply and demand, security of access, development problems, equity, market dynamics, by also taking into account the whole energy lifecycle including fuel production, transmission and distribution, energy conversion, and the impact on energy equipment manufacturers and the end-users of energy systems. Issues of energy efficiency and rebound effect must also be taken into proper account. In the short term, the aim should be to achieve higher energy efficiencies and increased supply from local energy sources, in particular renewable energy sources.