This dissertation explores changing forms of internationalism among the French and U.S. radical left from the 1960s through the late 1970s. In the 1960s, Vietnamese resistance to U.S. imperialism inspired French activists to forge an international antiwar alliance with U.S. activists opposing their government’s aggression. Together, they created a form of anti-imperialist internationalism based on the right of nations to self-determination. Despite transnational protest, the United States escalated the war, leading many activists to argue that the best way to aid Vietnamese national liberation was to translate that struggle into their own domestic contexts. In so doing, they triggered a wave of upheaval that reached new heights in May 1968. But when this anti-imperialist front faced repression and imprisonment in France and the United States, these same radicals began to advance individual rights alongside anti-imperialist revolution in the early 1970s. Once they learned of South Vietnam’s heightened repression of political dissenters, they grafted their new attention to rights onto the antiwar movement, demanding the restoration of civil liberties. Yet in arguing that South Vietnam violated fundamental democratic rights, anti-imperialist internationalism increasingly took the form of criticizing the internal affairs of a sovereign state. In this way, anti-imperialists lent legitimacy to a rival form of internationalism that shared the progressive aspirations of anti-imperialism but rejected nationalism in favor of human rights. When genocide, internecine war, and refugee crises in Southeast Asia undermined faith in national liberation in the late 1970s, former French radicals sided with the U.S. government to lead a global movement championing human rights against the sovereignty of nation-states like Vietnam. By tracing this history of solidarity with the Vietnamese liberation struggle from the 1960s to the 1970s, this dissertation explains how and why human rights came to displace anti-imperialism as the dominant form of internationalism. It shows that the Vietnam War was a truly global phenomenon, that the trajectory of the left in countries like France was powerfully shaped by developments in what was then called the Third World, and that the rise of human rights was closely connected to transformations within anti-imperialist internationalism.