IT all started with air mattresses.

Brian Chesky’s parents wanted just one thing for him when he graduated from the Rhode Island School of Design — that he get a job with health insurance. He tried that for a while with a design firm in Los Angeles, but he got fed up and packed up his Honda Civic and drove up to San Francisco to crash with his pal, Joe Gebbia, who agreed to split the rental of his house with Chesky. “Unfortunately, my share came to $1,150 and I only had $1,000 in the bank, so I had a math problem — and I was unemployed,” said Chesky. But they did have an idea. The week Chesky got to town, in October 2007, San Francisco was hosting the Industrial Designers Society of America, and all the hotel rooms on the conference Web site were sold out. So Chesky and Gebbia decided, why not turn their house into a bed and breakfast for attendees?

The problem was “we had no beds,” but Gebbia did have three air mattresses. “So we inflated them and called ourselves ‘Airbed and Breakfast,’ ” Chesky, 31, recalled for me in an interview. “Three people stayed with us, and we charged them $80 a night. We also made breakfast for them and became their local guides.” In the process, they made enough money to cover the rent. More important, though, it spawned a bigger idea that has since blossomed into a multimillion-dollar company and a whole new way for people to make money. The idea was to create a global network through which anyone anywhere could rent a spare room in their home to earn cash. In homage to its roots, they called the company Airbnb, which has grown so large, so fast that it is now the equivalent of a major global hotel chain — even though, unlike Hilton, it doesn’t own a single bed. And the new trend it set off is the “sharing economy.”

I first heard Chesky describe his company two years ago and thought it was a quaint idea that would find limited traction with niche travelers. I mean, how many people in Paris really want to rent out their kid’s bedroom down the hall to a perfect stranger who comes to them via the Internet? And how many strangers want to be down the hall? Wrong. Turns out there is an innkeeper residing in all of us!

On July 12, Chesky told me, “Tonight we have 140,000 people around the world staying in Airbnb rooms. Hilton has around 600,000 rooms. We will get up to 200,000 people per night by peak this summer.” Airbnb has 23,000 rooms and homes listed in New York City alone, and 24,000 in Paris. Worldwide, “we have listings in 34,000 cities and 192 countries,” added Chesky. “We are the largest short-term rental site of its kind in China today, and we have no office there.”