As we gear up for war in the Middle East and watch oil prices soar, it is easy to understand that energy is a big issue. We have to somehow wean ourselves off our dependence on oil--and the sooner, the better. What is less well known is the incredible magnitude of the worldwide energy challenge that is before us. The problem is not just oil. Somehow, within the next few decades we must find a new energy source that can provide a minimum of 10 terawatts (TW) of clean power on a sustainable basis and do this cheaply. To do this with nuclear fission would require no less than 10,000 breeder reactors. Assuming we don’t get it all from nuclear fission, where is that 10 TW of new power going to come from? Who will make the necessary scientific and engineering breakthroughs? Can it be cheap enough to bring 10 billion people to a reasonable standard of living? Can it be done soon enough to avoid the hard economic times, terrorism, war and human suffering that will otherwise occur as we fight over the dwindling oil and gas reserves on the planet? Energy may very well be the single most critical challenge facing humanity in this century.