Since the industrial revolution, progress has meant an increase in labour productivity. "Factor Four" describes a new form of progress, resource productivity, a form which meets the overriding imperative for the future (sustainability). It shows how at least four times as much wealth can be extracted from the resources we use. As the authors put it, the book is about doing more with less, but this is not the same as doing less, doing worse or doing without. In 1972, the Club of Rome published "Limits to Growth", which sent shock waves around the world by arguing that we were rapidly running out of essential resources. This Report to the Club of Rome offers a solution. It lies in using resources more efficiently, in ways which can already be achieved, not at a cost, but at a profit. The boo