Since the early 20th century, state and local governments have mandated vaccines to residents in their jurisdictions based on public health needs and to segments of the population most at risk, including children. Today, all 50 states require children enrolled in schools to be vaccinated against a number of preventable diseases. Though vaccines have been around for over a century and have been proven to protect people from infectious diseases and against communicable spread, an anti-vaccine movement of parents has been growing in the United States over the past decade or so, resulting in pockets of under-immunized communities and more frequent and widespread outbreaks of potentially serious diseases like measles. Professor Dorit Reiss of UC Hastings Law explains the advent of vaccine mandates in the United States and the constitutional framework for school mandates. She examines the various states’ exemptions to school mandates, some legislative responses to recent outbreaks, and enforcement and other measures to improve immunization rates among children.