As I pulled my overloaded Subaru up to a house in Ann Arbor, Mich., I paused a moment with an unsettling realization.

Inside the home - a lovely two-story brick Colonial on a quintessentially leafy street - was a couple I'd met just once before, for an hour. Based on that meeting, a few e-mails and a one-page agreement, we'd arranged to swap houses for the next nine months while I studied at the University of Michigan and they took an extended vacation in Seattle.

The what-ifs, I realized, were daunting. The Ann Arbor couple - Hans and Chris - seemed ideal house-swappers. But what if they weren't? What if Hans and Chris hated our house and wanted to come home? Or, more plausibly, what if my young children wreak the kind of havoc that I know they can?

House swapping, I came to learn, is all about faith. Trust in people - and do your homework - and the rewards are tremendous.

Hundreds of thousands of people around the world swap homes each year, and finding a horror story is almost as rare as a platypus. You are far more likely to hear tales of transcontinental friendships and astonishingly cheap vacations in what amounts to free accommodations.

I'd done two previous short house-swaps - for a lake cabin in Idaho and a condo in Whistler, British Columbia - and knew a bit about the trade-offs. Living in someone else's home - and opening your own to strangers - has its anxieties and discomforts. But for adventure and full cultural immersion, home exchanging opens a different world of travel.

House-swapping has been in vogue since at least the 1950s, propelled by the rise of affordable air travel and the affection for Europe that World War II GIs brought home.

It has exploded with the Internet age. An alphabet soup of professional agencies offer worldwide listings for small fees. Craigslist has a house-swap category, catering mostly to people looking for longer-term trades.

The concept is self-explanatory: a straight exchange of homes, for a fixed period. Most exchanges are between one and three weeks, and often include cars or bikes. Longer-term swaps require exchanges of utility bills and, in some cases, notice to home insurers.

For peace of mind, Nicole Frank, who writes at HomeExchanger.blogspot.com, strongly recommends using an agency and avoiding Craigslist, the free Web site where individuals can post exchange offers. When things go wrong, the agency has credit-card information to track down an exchanger, and subscribers are often house-swap veterans.

As a general rule, "act as if your boss lent you their country house for the weekend," Frank says. "If you do, you'll be respectful."

John Mensinger, a veteran house-swapper who writes on Homeexchangeguru.com, has a few golden rules. Minimize risk by locking up valuables, meeting your swappers, and doing basic homework on them and their hometowns. Have a "broad view" of knowing you may not get a totally equal exchange.

"You have to have a generous spirit," Mensinger says. "You have to know little things are going to go wrong."

Our Michigan swap came together after I received a journalism fellowship at the University of Michigan for the 2008-09 academic year.

My wife and I realized we couldn't rent our bungalow in the Wallingford neighborhood for the amount of our mortgage, so I posted an ad seeking a home exchange on the Ann Arbor Craigslist.

Hans and Chris responded while I was house-hunting in Michigan, so we had what amounted to a date.

Retired and well-traveled, they'd been looking for a long-term house swap. They have a tribute to Jerry Garcia on their living-room mantel and an exhaustive book collection.

Chris was more concerned about fixing her house for us than vice versa. "I think we are somewhat adventurous, which is a mindset that some folks don't have," Chris wrote in an e-mail.

As nice as they seemed, I'm in the trust-but-verify set. I looked up property records and checked Hans and Chris for bankruptcies and criminal convictions.

House-swappers will tell you the hardest part is prepping your house for exchanges. I spent weeks on small jobs, including installing a new toilet and an outdoor-watering system.