Online marketplaces aren't a new idea. Yet over the past few years, they have (re)emerged as a preferred channel for consumers, small businesses, and a growing number of enterprise buyers. For brands and other sellers, they offer a low-cost way to reach online customers or enter new markets but also less control over a company's brand and the user experience. For operators, orchestrating an ecosystem of buyers, sellers, and technology partners requires mastery of eCommerce, brand building, and demand gen — but also offers unique economic benefits of running a digital platform business. This report summarizes our research on consumer and business marketplaces and explains how to understand buyer preferences and succeed as a seller or operator.