Explores the line between free speech protected by the First Amendment and unprotected incitement to imminent lawless action. Free Speech and Incitement in the Twenty-First Century explores the line between free speech and incitement, which is a form of expression not protected by the First Amendment. Incitement occurs when a person intentionally provokes their audience to engage in illegal or violent action that is likely to, or will, occur imminently. This doctrine evolved from World War I through the Cold War and the civil rights movement era, culminating in a test announced by the US Supreme Court in Brandenburg v. Ohio (1969). Since the 1970s, this doctrine has remained largely unchanged by the Supreme Court and, as such, has received relatively little academic or media attention. Since the late 2010s, however, violence at political rallies, armed protests around Confederate statues, social unrest associated with demonstrations against police, and an attack on the US Capitol have led to new incitement cases in the lower courts and an opportunity to examine how incitement is defined and applied. Authors from different perspectives in Free Speech and Incitement in the Twenty-First Century help the reader understand the difference between free speech and incitement.