In two centuries of vaccination in the U.S., the last five decades constituted a unique era. American children received more vaccines than any previous generation, and laws requiring their immunization against a litany of diseases became common. Vaccination rates soared, preventable infections plummeted, and popular acceptance of vaccines remained strong--even as an increasingly vocal cross-section of Americans questioned the safety and necessity of vaccines and the wisdom of related policies. This dissertation examines how and why, between the 1960s and 2000s, Americans came to accept the state-mandated vaccination of all children against a growing number of infections despite the growing prominence of vaccine doubts. I argue that vaccines and vaccine policies fundamentally changed the ways health experts and lay Americans perceived the diseases they were designed to prevent. Second, I demonstrate that vaccination policies and their acceptance throughout this period were as contingent on political, social, and cultural concerns as they were on scientific findings. Thirdly, I show how, as new vaccine policies took shape, feminism, environmentalism, and other social movements laid challenge to scientific and governmental authority, with profound--but previously overlooked--implications for how Americans perceived vaccination. Finally, I argue that the relationship between vaccination beliefs and political ideology is more complex than historians have heretofore asserted, for selective and blanket vaccination doubts at the end of the twentieth century were as informed by leftist critiques of capitalism and social hegemonies as by traditional American libertarian ethics. This work draws on a diverse set of sources, including presidential archives; government agency records and publications; popular and scientific print media; television broadcasts; newsletters; internet archives; documents and publications at chiropractic libraries; and the personal files of vaccine scientists and critics. It contributes to the histories of disease, women, the environment, and health politics, as well as the sociology of social movements. By placing public health knowledge in historical context, this dissertation illuminates the many meanings of vaccination that lay between that of gold-standard disease preventive and hotly contested enterprise at the end of the twentieth century and the beginning of the twenty-first.