The theoretical—and market—background against which the intermediary liability debate developed has changed considerably since the first appearance of online intermediaries almost two decades ago. These changes have been reflected—or will soon most likely be reflected—in changing policy approaches. The role of Online Service Providers (OSPs) is unprecedented for their capacity to influence the informational environment and users’ interactions within it. The ethical implications of OSPs’ role in contemporary information societies are raising unprecedented social challenges. The decisions made by these platforms increasingly shape contemporary life. Therefore, whether and when access providers and communications platforms such as Google, Twitter, and Facebook are liable for their users’ online activities is a key factor that affects innovation and fundamental rights. There are emerging legal, policy, and ethical issues facing online intermediaries that have so far received various inconsistent answers even within the same jurisdiction. To better understand the heterogeneity of the international online intermediary liability regime, The Oxford Handbook of Online Intermediary Liability is designed to provide a comprehensive, authoritative, and ‘state-of-the-art’ discussion of this topic. This book will review fundamental legal issues in online intermediary liability, while also describing advances in intermediary liability theory and identifying recent policy trends.