Ecological design, the marriage of nature and technology, can be applied at all levels of scale to create revolutionary forms of buildings, landscapes, cities, and technologies. Some examples include sewage treatment plants that use constructed marshes to purify water; agricultural systems that mimic and merge with their surrounding landscapes; industrial "ecosystems" in which waste from one productive process becomes fuel for the next. The authors weave together case studies, personal anecdotes, dialogues, images, and theory to provide a thorough treatment of the concept of ecological design. In the process, they present and explain a series of design principles that can help build a sustainable world with increased efficiency, fewer toxics, less pollution, and healthier natural systems.