Abstract
Long-term limits to growth in energy will be imposed not by inability to expand supply, but by the rising environmental and social costs of doing so. These costs will therefore be central issues in choosing long-term options. Fusion, like solar energy, is not one possibility but many, some with very attractive environmental characteristics and others perhaps little better in these regards than fission. None of the fusion options will be cheap, and none is likely to be widely available before the year 2010. The most attractive forms of fusion may require greater investments of time and money to achieve, but they are the real reason for wanting fusion at all.