Although the term ‘resource efficiency’ is widely used in sustainability discus ‐ sions, there is a need to explain its background, given that there is no universally accepted definition. ‘Resource efficiency’ in this book refers to the lowest possible use of natural resources to achieve an economic outcome with a minimum of environmental impact. This contributes to decoupling of economic growth and human welfare from resource use and environmental degradation. Life cycle approaches offer a way to enhance resource efficiency by identifying inefficiencies and impacts along the life cycle of products and services.