The Natural Step (TNS) is a way of examining the concept of sustainability and taking action to achieve it. More information on this framework can be found on the Natural Step homepage, or within the TNS Framework Guidebook (PDF - 650 KB).  The following are quotes from the TNS website.

"Creating a sustainable world means creating new ways for people to live and thrive -- while keeping the planet balanced and healthy. Our principles of sustainability drive path-breaking models and tools that pass these three tests: Is it good for business, good for society and good for the environment? "

"The Natural Step provides a visionary blueprint for a sustainable world. Our upstream approach means we address problems at the source and turn them into opportunities for innovation. As an international advisory and research organization, we work with some of the largest resource users on the planet to create solutions, models and tools designed to accelerate global sustainability."