What is often called the “energy crisis” or “energy problem” is basically an environmental problem (one of pollution, sustainability, climate change), which presents a challenge, the “Energy Challenge”. This challenge is to find a mix of energy resources that will allow the types of life styles that people desire, for a global population that may reach 10 billion. History shows that, grosso modo, the higher the standard of living the slower the population growth (which can even become negative; cf. Japan today). Therefore, the sooner people reach a higher standard of living, which requires an increase in power available to and affordable for them, i.e., their energy consumption, the sooner the world population will stabilize and the smaller the challenge. Thus, we have here a double challenge, the faster we face the challenge and meet it, the smaller it is!