Often when people think of policy for long-term sustainability they think of energy supply and not energy demand. What comes to mind often are new sources of supply on the very edge of technology, such as shale gas and deep-sea oil resources; or it may be renewable energy sources, such as hydro, wind, solar, geothermal and biofuels. But if people focus exclusively or excessively on supply, they are overlooking the demand side. How much energy must we produce in order to meet our human and economic needs? What assumptions are we making about future energy demand? In regard to a particular energy project going through an environmental impact assessment process, how do we evaluate whether the project is necessary?