Freedom of speech is central to the liberal democratic tradition. It touches on every aspect of our social and political system and receives explicit and implicit protection in every modern democratic constitution. It is frequently referred to in public discourse and has inspired a wealth of legal and philosophical literature. The liberty to speak freely is often questioned; what is the relationship between this freedom and other rights and values, how far does this freedom extend, and how is it applied to contemporary challenges? This handbook seeks to answer these and other pressing questions. It provides a critical analysis of the foundations, rationales, and ideas that underpin freedom of speech as a political idea, and as a principle of positive constitutional law. In doing so, it examines freedom of speech in a variety of national and supra-national settings from an international perspective.