Air B&B has definitely evolved over the years. The original concept was just as StMartinFan stated; renting out an unused room in your home for a little extra income. As it has become more popular, more traditional rental properties have started advertising on the site as well. My wife and I owned a B&B in Maine for 10 years and feel lucky that we got out when we did. The landscape in the lodging industry has changed dramatically from what is was 15 years ago.