A growing number of travelers want their journeys to benefit the people and places they visit. But the line between helping and hurting isn't always apparent. G. Jeffrey MacDonald reports from Morocco on the revelations, challenges, and rewards of trying to stick to the moral high road

Ten years ago, life in Morocco was, in many respects, different than it is today. Mules, a staple of commercial transport in this developing nation, were 50 percent cheaper than they are now. Marrakech real estate sold for a fraction of today's prices. Mountainside Berber villages near Imlil had no electricity, no education for most children, and no quick way to reach a hospital in an emergency. Tourism has changed all of that.

Moroccans are experiencing a global twenty-first-century reality: Travel is altering lives, for better and for worse, in communities across the planet where voyagers hang their hats. It's a function of scale. With air travel becoming ever more accessible, international tourism has exploded from 25 million visits in 1950 to 842 million in 2006. The World Tourism Organization expects that by 2020, 1.6 billion people will be vacationing internationally.

With visitors comes cash: Tourism receipts totaled $730 billion in 2006, not including transportation, which makes travel one of the world's largest industries. And that, according to social and environmental activists, puts travelers in an unprecedented position to relieve—or aggravate—some of the world's most pressing problems. It all depends on how they use their expanding clout.

"It's inevitable that we're going to have an impact," says Tricia Barnett, director of Tourism Concern, a Britain-based lobby for ethical travel. "You can't avoid it."

To date, tourists as a group haven't always had a stellar record. They've flocked by the millions to Egypt's Luxor, threatening the integrity of its many antiquities. Venice faces an overcrowding and pollution crisis, exacerbated by an influx of some 100,000 tourists a day in high season. And the World Monuments Fund has in recent years repeatedly named Chile's Rapa Nui one of the world's 100 Most Endangered Sites. The primary reason: uncontrolled tourism.

International organizations have tried to help. For instance, UNESCO lists 851 World Heritage Sites in a bid to make sure they're forever revered as treasures. But such commendable efforts have sometimes had deleterious effects, according to Stefaan Poortman, international development manager at the California-based Global Heritage Fund, a nonprofit that works to preserve important archaeological and cultural sites. "When developing nations get a World Heritage designation, it's often a double-edged sword," Poortman says. "While it can bring a flow of resources and people, often the value and finiteness of this asset are not protected. So it becomes a kind of 'get it while you can' philosophy" (see "Making a List and Checking It Twice").

Against this checkered backdrop, the onus is increasingly falling on individual travelers—even luxury junkies—to craft trips that have a positive effect on people and places without compromising the traveler's enjoyment. Resources for doing so include books such as Tourism Concern's The Ethical Travel Guide and Lonely Planet's Code Green, both new in 2006. Twice in the past year, this magazine has published lists of questions to help travelers ferret out which hotels are socially responsible and which just talk a good game. (For a list of ethical-travel resources, see "You Are Not Alone.")