Often hailed as the "first freedom," free speech is the bedrock of democracy, the enemy of tyranny, and the gateway to enlightenment. Research reveals a strong correlation between freedom of speech and democracy, innovation, and advancements in human rights, as well as reductions in conflict, corruption, and discrimination. But for all its benefits, free speech remains a challenging, controversial, and often counterintuitive principle, easily subject to erosion in times of social and political upheaval. And today, in democracies and authoritarian states around the world, freedom of speech is now on the retreat. In Free Speech, Jacob Mchangama traces the long, contested history of a powerful idea, beginning with its origins in the intellectual ferment of classical Athens, where it enabled the development of the world's first democracy.