What balance should be struck between freedom of expression, as an essential right and value of any democratic society, and other constitutional rights when facing falsehood and extreme speech? How are Europe and legislators around the world reacting to the rise of online disinformation and hate speech, in the wake of mounting evidence of adverse effects on democratic processes? What is the most effective approach to address and tackle harmful practices over the Internet, if any? These are some of the pivotal questions that this book seeks to explore. The potentially global scale and the unprecedented velocity of the dissemination of false and extreme content raise concerns that are specific to our digital age. It is the Authors' belief that the answers to such questions plunge their roots in the origins of contemporary constitutionalism, with the paradigm of the constitutional traditions of Europe and the United States. Specifically, the right to freedom of expression, its development and subsequent application to the digital dimension constitute the starting ground of the analyses here proposed.