The freedom of assembly has been at the heart of some of the most important social movements in American history: antebellum abolitionism, women's suffrage in the nineteenth and twentieth centuries, the labor movement in the Progressive Era and after the New Deal, and the Civil Rights movement. Claims of assembly stood against the ideological tyranny that exploded during the first Red Scare in the years surrounding the First World War and the second Red Scare of 1950s' McCarthyism. Abraham Lincoln once called “the right of peaceable assembly” part of “the Constitutional substitute for revolution.” In 1939, the popular press heralded it as one of the “four freedoms” at the core of the Bill of Rights. And even as late as 1973, John Rawls characterized it as one of the “basic liberties.” But in the past thirty years, assembly has been reduced to a historical footnote in American law and political theory. Why has assembly so utterly disappeared from our democratic fabric? This Article explores the history of the freedom of assembly and what we may have lost in losing sight of that history.