On December 20, 2015, a mountain of urban refuse collapsed in Shenzhen, China, killing at least 69 people and destroying dozens of buildings. The disaster brought to life the towers of waste depicted in the 2008 dystopian children's movie WALL-E, which portrayed the horrible yet real idea that our trash could pile up uncontrollably, squeezing us out of our habitat. A powerful way to transform an existing city into a sustainable one—a city that preserves the earth rather than ruining it—is to reduce all the waste streams and then use what remains as a resource. Waste from one process becomes raw material for another.