Technical progress has long been known as a major spur to economic growth. But is it also a key to solving environmental problems arising from such growth? The evidence points that way, according to a study carried out at Imperial College, London. In many cases new technologies and practices have proved less costly than polluting alternatives they displace. Researchers reviewed pollution control practices and came up with a dynamic ready reckoner for assessing costs and effectiveness over time of alternative technical choices. Surprising savings and lessons emerged when they tested this framework in the context of actual cases.