Sample trip: Collect data on river otters in Chile.
Cost: $1,560 for two weeks, plus airfare.
The gist: Trips are led by researchers who have been at the same site for years and offer good local contacts and expertise. But remember that scientific fieldwork can be monotonous—no matter how appealing the topic may seem, ask questions beforehand about a typical day's activities.
800/776-0188 or 978/461-0081; www.earthwatch.org
Sample trip: Teach conversational English in Ghana.
Cost: $2,350 for three weeks, plus airfare.
The gist: Some sites have paid local staff; others do not. Some focus on social work, some on construction and renovation projects. Be sure to do your homework in advance to find the trips that are the best organized.
800/487-1074 or 651/407-6100; www.globalvolunteers.org
Habitat for Humanity
Sample trip: Renovate low-income housing in Kyrgyzstan.
Cost: $1,400 for two weeks, plus airfare.
The gist: Expect to work closely with a group of American travelers. Note that Habitat is a faith-based organization, though not an evangelical one.
800/422-4828 or 229/924-6935, ext. 2549; www.habitat.org
Volunteers for Peace
Sample trip: Organize and staff a multicultural arts festival in Croatia.
Cost: $200 for two weeks, plus airfare.
The gist: The bargain price means trips are spartan, and there is little vetting of local project managers, so quality will vary from site to site. You'll probably camp out on a floor somewhere, cobble together meals, and solve any problems yourself. Do a little extra research, though, and you can get a great volunteer trip for next to nothing.
Many mainstream travel providers donate money, time, and organizational support to a range of causes; if you don't want a hands-on volunteer experience, you can still do some good when you travel by booking with them. Here, some of the most prolific givers in the industry.
• True to its name, Conservation Corporation Africa (888/882-3742; www.ccafrica.com) doesn't just own top safari lodges; it has transformed the Phinda Game Reserve from 34,000 acres of ravaged South African land into a lush stamping ground for the Big Five, and also started the nonprofit Africa Foundation to build clinics and preschools and provide university scholarships to students in rural communities.
• Micato Safaris (800/642-2861; www.micato.com), a leading outfitter in East Africa, supports five Kenyan orphanages through its nonprofit arm, America Share. With help from former guests and corporate sponsors, it supplies more than 900 children with clothes, medicine, and school supplies.
• Each year, the southern Africa-based Wilderness Safaris (www.wildernesssafaris.com) invites poor young people from Botswana, Namibia, and Malawi to about 20 of its camps, offering programs in health and environmental education. A portion of all trip costs goes to the company's wildlife emergency fund.
• The nonprofit African Conservancy (760/945-7571; www.africanconservancy.org) supports anti-poaching efforts, organic farming cooperatives, and wildlife education programs on the continent. Through its new Traveler's Legacy Program, you can book customizable flying safaris that provide wildlife viewing and a firsthand look at the conservancy's programs. At the end of the trip, you select where to allocate a $20-a-night portion of your trip's cost.
• For five years, Asia Transpacific Journeys (800/642-2742; www.asiatranspacific.com), which offers group and custom trips throughout Southeast Asia and the South Pacific, has assisted in Burmese refugee camps along the Thai border. Through woodworking, pottery, and bicycle-repair workshops, the company's foundation teaches practical skills to orphans and children who have been separated from their families.
• The exclusive Turtle Island resort (877/288-7853; www.turtlefiji.com), in the remote reaches of the Fiji Islands, hosts annual health clinics with visiting medical specialists (all former guests), has built a secondary school, and is at work on establishing the area's first permanent medical facility. It also constructed two budget lodges and turned over ownership to villagers.
• In the seven years since it founded the Galápagos Conservation Fund, Lindblad Expeditions (800/397-3348; www.expeditions.com) has raised more than $2 million for conservation and education projects. The outfitter also works with the nonprofit organization Oceanites to bring guest scientists on its Antarctic ships, sponsoring research and allowing passengers to assist in projects.
• Tour operator Tauck World Discovery (800/788-7885; www.tauck.com), in collaboration with the family-run Tauck Foundation, gives thousands of dollars in grants each year to youth programs, preservation organizations, and national parks. Last summer, the company offered guests on its Yellowstone National Park trips the opportunity to spend a few hours doing maintenance work in the park. The program will expand this summer to include volunteer options in Glacier National Park and the Grand Canyon.