PENNY-WISE.(The Talk of the Town)

The notion that we live in a global economy is now a commonplace. Supply chains extend halfway around the planet, and no respectable corporation would dare show its face without at least pretending to have a well-defined global strategy. The funny thing about the global economy, though, is how much of the globe has been left out of it. Four billion people still earn less than four dollars a day, and as far as the global economy is concerned they hardly exist--except, of course, as cheap labor. After all, if you were the C.E.O. of a big company, whom would you rather have as customers: the rural poor in Uttar Pradesh or upscale suburbanites in greater Phoenix?

But perhaps it makes better sense for companies to see the poor as patrons worthy of their solicitations. Though developing nations don't have much money on a per-capita basis, together they control enormous sums; the ten biggest developing countries have about fourteen trillion dollars in annual purchasing power. Most corporations assume that the world's poor are so preoccupied with getting by that they're indifferent to the allure of consumer goods or new technology, but the evidence suggests that poor consumers are similar to rich ones: they like to shop. "Poor people want quality services, they want high standards for their products, and they want them at an affordable price," C. K. Prahalad, the author of a new book about fighting global poverty called "The Fortune at the Bottom of the Pyramid," told me recently. "This is a huge opportunity for businesses."

It may seem improbable that you can make money by selling to people who don't have much, but, as Prahalad demonstrates, companies that have actually bothered to try are flourishing. Unilever helped create the shampoo market in India, and now owns a large share of it. Hindustan Lever has built a lucrative business in Africa and India selling brand-name consumer goods, from lotion to salt. Casas Bahia, a department-store chain, now sells more than five billion dollars' worth of brand-name electronics and appliances to working-class Brazilians every year. Big companies often disdain what they think of as the low-end market, because they make a lot less money on each sale than they do selling high-end goods. But, because of the sheer size of that market, they can still make a lot of money on it. This isn't exactly a radical concept: it's what companies like Pillsbury, Quaker Oats, and Singer Sewing Machine did in America in the nineteenth century and, to a certain extent, what Wal-Mart is doing now.

Bringing technology to local farmers and merchants in developing countries has proved lucrative as well. In South Africa, Standard Bank has set up an A.T.M. banking network for low-income customers, which has widely expanded their access to credit. The Indian conglomerate I.T.C. has equipped hundreds of homes in the rural province ...