How do you put a price tag on nature -- on its worth, on the cost of protecting it, and on the expenses incurred by destroying it? In an effort to marry wise environmental policy with sound economics, more and more conservationists are seeking to answer that question. In The New Economy of Nature, Katherine Ellison, a Pulitzer Prize-winning journalist, and Gretchen C. Daily, one of the world's leading ecologists, track the efforts to create an economy that recognizes the value of natural systems. Sometimes, creating that new economy requires looking at cost and benefit in a whole new way, as happened in Napa, Calif., when residents and government agencies set out to solve the problem of regular river flooding. Read about the Napa solution, in an excerpt from The New Economy of Nature, only on the Grist Magazine website.