An emerging area of economics aims to put a price on nature as a way of justifying preserving it in societies dominated by the wisdom of markets. A mountain stream, for example, provides many economic benefits beyond people who own property near it or drink water from it. The same is said of bees that pollinate our food, wetlands that cleans water, and trees that drink up carbon dioxide. If nature were a corporation it would be a large cap stock. Putting a precise tag on something long seen as free is a conceptual leap. However many large companies are starting to realize the extent to which their profits rely on well-operating ecosystems. An economist and sustainability professional discussed ecosystem services and the economic value of the natural world.