Jurisdiction is the foundational concept for both national laws and international law as it provides the link between the sovereign government and its territory, and ultimately its people. The internet challenges this concept at its root: data travels across the internet without respecting political borders or territory. This book is about this Jurisdictional Challenge created by internet technologies. The Jurisdictional Challenge arises as civil disputes, criminal cases, and regulatory action span different countries, rising questions as to the international competence of courts, law enforcement, and regulators. From a technological standpoint, geography is largely irrelevant for online data flows and this raises the question of who governs “YouTubistan.” Services, communication, and interaction occur online between persons who may be located in different countries. Data is stored and processed online in data centres remote from the actual user, with cloud computing provided as a utility. Illegal acts such as hacking, identity theft and fraud, cyberespionage, propagation of terrorist propaganda, hate speech, defamation, revenge porn, and illegal marketplaces (such as Silkroad) may all be remotely targeted at a country, or simply create effects in many countries. Software applications (“apps”) developed by a software developer in one country are seamlessly downloaded by users on their mobile devices worldwide, without regard to applicable consumer protection, data protection, intellectual property, or media law. Therefore, the internet has created multi-facetted and complex challenges for the concept of jurisdiction and conflicts of law. Traditionally, jurisdiction in private law and jurisdiction in public law have belonged to different areas of law, namely private international law and (public) international law. The unique feature of this book is that it explores the notion of jurisdiction in different branches of “the” law. It analyses legislation and jurisprudence to extract how the concept of jurisdiction is applied in internet cases, taking a comparative law approach, focusing on EU, English, German, and US law. This synthesis and comparison of approaches across the board has produced new insights on how we should tackle the Jurisdictional Challenge. The first three chapters explain the Jurisdictional Challenge created by the internet and place this in the context of technology, sovereignty, territory, and media regulation. The following four chapters focus on public law aspects, namely criminal law and data protection jurisdiction. The next five chapters are about private law disputes, including cross-border B2C e-commerce, online privacy and defamation disputes, and internet intellectual property disputes. The final chapter harnesses the insights from the different areas of law examined.