When things go seismic deep in the global economy, stock exchanges around the world react like so many volcanoes. From New York’s Wall Street to Tokyo’s Kabutocho district, their eruptions are the manifestations of trillion-dollar forces roiling under the surface, spouting volatility, and creating panic in a global market gone Vesuvius.

When things go seismic, watch out for the metaphor hose-down from economists, journalists, and shrieking CNBC V.J.’s trying to convey a picture bigger than what you can see by just riding the three-digit updrafts and free falls. In a delicate balance of dependence and autonomy, the exchanges of the world constitute tangible grounding mechanisms for spooked investors. They are rooms in which buyers and sellers trade by sets of rules that are, in the end, all that keep the global market from dissolving into chaos after each morning bell. The stability flows from how each market is simultaneously connected to the shifts of global capital yet also able to generate transactions on its own local terms.

An exchange must assure two things: that all serious buyers and sellers are represented and that the products of all sellers are deliverable and of some demonstrable quality. The same assurances are required whether cattle are changing hands in Argentina or shares of Sultan Center Food Products are being traded in Kuwait.

On a quiet, tree-lined street in Kathmandu—just up the road from the Freak Street market, fragrant with spices and diesel fumes and mountain-trekking hippies—sits the Nepal Stock Exchange. Beneath whirring fans, traders scrawl on whiteboards their “bids” and “asks,” worth about a million dollars a day, for such companies as Everest Bank and Butwal Power.

Meanwhile, the New York Stock Exchange, the biggest of them all, carefully maintains the elaborate illusion of a bustling trading floor, even though that space functions mostly as a TV studio and tourist attraction for visiting V.I.P.’s unaware of the vast computer networks that actually handle the transactions. An average of $100 billion worth of trades clears this legendary center of finance daily—only a quarter of the money that circulates through the world’s markets every 24 hours.

Electronic trading knows no geographic constraints, so nowadays stock exchanges can be found in places better known for thousand-year-old eggs than for nest eggs. The explosion of trading across the globe has created wealth in some of the most persistent pockets of poverty and produced waves of volatility, as when this year’s U.S.-subprime-mortgage tsunami hit beaches in South Korea, Australia, and Indonesia. In an era when billions zip from continent to continent in milliseconds, it is exhilarating to recall that modern capitalist economy is built on a mysterious faith that, in the public forum of the exchange, the other guy or gal is not going to screw you. An absence of trust has plagued one of the world’s smallest stock exchanges, in Douala, Cameroon. Haunted by the country’s enduring reputation for corruption, the Douala exchange has hosted trades in shares of only one company—a local bottled-water producer—since opening in April 2003. Meanwhile, the end of a corrupt dictatorship has produced a boom in Kenya. There are more ways than ever for U.S. investors to chase those returns: One can give cash directly to a non-U.S. broker or buy one of a dizzying array of securities, such as shares in specially structured mutual funds. The Federal Reserve estimates that U.S. investors hold more than $4 trillion worth of foreign equity, much of it in emerging markets in Asia and Latin America.