MUMBAI, India — At the edge of India’s greatest slum, Shaikh Mobin’s decrepit shanty is cleaved like a wedding cake, four layers high and sliced down the middle. The missing half has been demolished. What remains appears ready for demolition, too, with temporary walls and a rickety corrugated roof.

Yet inside, carpenters are assembling furniture on the ground floor. One floor up, men are busily cutting and stitching blue jeans. Upstairs from them, workers are crouched over sewing machines, making blouses. And at the top, still more workers are fashioning men’s suits and wedding apparel. One crumbling shanty. Four businesses.

In the labyrinthine slum known as Dharavi are 60,000 structures, many of them shanties, and as many as one million people living and working on a triangle of land barely two-thirds the size of Central Park in Manhattan. Dharavi is one of the world’s most infamous slums, a cliché of Indian misery. It is also a churning hive of workshops with an annual economic output estimated to be $600 million to more than $1 billion.

“This is a parallel economy,” said Mr. Mobin, whose family is involved in several businesses in Dharavi. “In most developed countries, there is only one economy. But in India, there are two.”

India is a rising economic power, even as huge portions of its economy operate in the shadows. Its “formal” economy consists of businesses that pay taxes, adhere to labor regulations and burnish the country’s global image. India’s “informal” economy is everything else: the hundreds of millions of shopkeepers, farmers, construction workers, taxi drivers, street vendors, rag pickers, tailors, repairmen, middlemen, black marketeers and more.

This divide exists in other developing countries, but it is a chasm in India: experts estimate that the informal sector is responsible for the overwhelming majority of India’s annual economic growth and as much as 90 percent of all employment. The informal economy exists largely outside government oversight and, in the case of slums like Dharavi, without government help or encouragement.

David Fuller's view I really do admire the exemplary work ethic of these people. Just think what they could achieve with better education and infrastructure.