This lecture was given at the American Academy in Berlin and it is an expanded version of an article published in the Bulletin of the Atomic Scientists. In it, Amory Lovins explains how energy efficiency measures can have a lasting impact on climate and the environment. Lovins’ answers the question, what can we do to stop climate change?” He points out that saving energy is cheaper than buying it, a concept that makes environmental and economic sense. He argues that the climate problem is not necessary or economically sensible. It is an artifact of wasted energy and money. When we take steps to save energy, we will also be saving money and protecting the environment.”