Chapter 3 explores the structure of digital platforms, covering their definition, business models, characteristics, issues, and regulatory frameworks. It begins by outlining the three tiers of digital platforms: communication platform (the internet), content platforms (operating systems), and application platforms (apps). It then discusses the businesses and challenges faced by the four major platform companies—Apple, Google, Amazon, and Meta. Next, it elaborates on key characteristics of digital platforms, including two-sided markets, attention economy, network externalities, and natural monopolies. Finally, the chapter addresses issues related to digital platforms, such as personal information and market dominance, and introduces the EU’s regulatory measures, including Digital Market Act (DMA) and the Digital Services Act (DSA).