This book traces the history, politics, and ethics of mandatory childhood vaccination policy in America, with close attention to recent legislative changes in California. California was the first US state to ban unvaccinated children from school in response to parents refusing vaccines. The new policy kick-started immunization rates, but also ignited polarizing debates about whether government should restrict people's liberty to promote public health. Other US states, and other countries, are watching California carefully: should they follow in its footsteps? Using original interviews with politicians, activists, technical experts, and civil society organization representatives, Mark C. Navin and Katie Attwell unpack the causes and consequences of cracking down on vaccine refusal in contemporary America.