Just back from her own hands-on experience, Dorinda Elliott introduces this surging movement. Plus: Teaching—and learning—in Cambodia, stove makeing in Peru, and romancing a reef in the Bahamas

I am stirring cement outside a mud house in a Peruvian farming community, wondering, just a little bit, why I am here. This is, in fact, my hands-on introduction to voluntourism; one of the family's sons is soaking bricks in water, while Mercedes, who runs the volunteer program, is prepping the kitchen's dirt floor. I don't speak Spanish, so I can't learn much about these people's lives except what I can see—from the outhouse, to the donkeys laden with jugs of milk for the tiny cheese-making operation, to the room upstairs where the family of six sleeps, with a TV rigged for reception with aluminum foil at the end of the antenna. Nor am I an expert in building. So why do they need me to help them build a stove?

Combining volunteer work with holidays was once the domain of nonprofits, small adventure companies, and granola-crunching backpackers—a bit like me out there in the Peruvian highlands. But these days, a lot of us are hoping to give back when we travel. According to a poll conducted by Condé Nast Traveler and MS-NBC, only fourteen percent of Americans have taken a volunteer holiday, but fifty-five percent say they would like to. And of those who have gone on volunteer trips, ninety-five percent say they are likely to do it again. "Travelers are looking for a sense of purpose in their leisure activities," says Brian Mullis, president of the Sustainable Travel International, which advises travel companies on voluntourism. "They are looking at new ways of distributing wealth. The age of checkbook philanthropy is morphing into the age of participatory philanthropy."

But does spending a few days as a volunteer in Peru or Timbuktu really do any good, or is it just another way for us spoiled First World travelers to assuage our guilt? It's often difficult to assess which projects are worthy—not to mention how much of the traveler's money is going to the local community. What is the value of an inexperienced volunteer showing up to teach English, only to be replaced by another unskilled person a few days later? There are certainly volunteer travel programs—even well-intended ones—that don't actually help much. But when done right, volunteering can both contribute to local communities and be life changing for the traveler. "An important part of what comes out of voluntourism is social capital: It breaks down stereotypes," says David Clemmons, founder of voluntourism.org, a nonprofit that offers tips on choosing volunteer trips. "For the traveler, it can help you retool and rethink your life philosophy, and the local people end up with a different image of foreigners. Is that worth the thousand dollars you paid to build that stove? You betcha!" (For some of Clemmons's tips, see cntraveler.com/makeadifference.)