
Amazon famously began life as an online bookseller, but 20 years later there are few products you can’t buy on the site. For many goods, the company acts as a traditional retailer, earning a profit through markups. Other goods are offered by third-party sellers—merchants who pay to use Amazon as a sales platform, much as people pay to sell items on eBay. Platform business models, which use technology to link buyers and sellers, have never been hotter. Examples include Uber and Airbnb (which link passengers with drivers and travelers with lodgings, respectively) and technology companies such as Facebook, Apple, and Twitter (which open their ecosystems to outside software and app developers). Venture capitalists love the platform model, because it lets companies scale up with limited funds: Airbnb, for instance, was able to grow far more quickly as a matchmaker than if it had had to build and operate hotels.