Have you ever wondered what differentiates an Airbnb from a traditional hotel? Or an Uber from a city taxi service? These are some of the many popular platforms that have come to dominate the world of business in the past decade. These platforms are typically asset-light (Airbnb does not own a single hotel, nor does Uber a taxi) but have enough market power to lead their respective industries. Typically, such platform business firms intermediate between different sets of users, leverage network effects to grow the market, and in some markets, dominate industries, leveraging winner-takes-all economies. This chapter introduces the platforms as unique business models and distinguishes them from traditional businesses.