This book is devoted to a number of Americans who distinguished themselves in promulgating the idea of free speech in the 20th century. Most of these people were jurists: justices of the US Supreme Court and professors of law, therefore it is the representatives of these two groups who are given special attention here. However, the text also discusses the contribution of people representing other professions, inter alia philosophy and political science. It is to be hoped that the book will prove useful for a large group of readers interested in free speech issues, including – apart from journalists, politicians or NGO activists – also teachers and students of journalism, mass communication, law, history, or political science. Free Speech Defenders in Twentieth Century United States is the second of a series of texts on various aspects of freedom of expression published by the Nicolaus Copernicus University Press in Toruń. The first book of the series: From Milton to Mill: Classic Defenders of Freedom of Speech appeared in 2012. Both texts will be followed by the book entitled Freedom of Speech and Other Human Rights.