This chapter explores the history of Americans’ opposition to their country’s military involvement in Vietnam. Energized by the escalation of the conflict, and the emergence of the wider student New Left, the relatively modest protests that had taken place in the early 1960s soon burgeoned into a genuine mass movement: by the time the Paris Peace Accords were signed in 1973 some 6 million Americans had taken to the streets or engaged in other forms of dissent. Highlighting the diversity of activists and the range and creativity of their tactics, the movement’s vital – if sometimes prickly – relations with contemporaneous social movements, and its wide geographical reach, the chapter concludes by evaluating the legacy and impact of American opposition to the war. While the protests certainly helped to shape the nation’s political culture – not least by inspiring subsequent social activism on both the left (gay liberation) and right (the early anti-abortion movement) – it remains far from clear what role, if any, domestic opposition to the Vietnam War had on the eventual outcome on the conflict in southeast Asia.