In the United States, many vaccine-preventable disease rates are at an all-time low. Low disease rates have been achieved through high rates of immunization coverage. Vaccination requirements for school and child care attendance have been recommended by the independent Task Force on Community Preventive Services based on systematic review of immunization interventions. These requirements have been determined to be effective in reducing vaccine-preventable disease and improving immunization coverage rates in all at-risk populations. At the same time, complacency, increasing vaccine costs, vaccine shortages, and the potential risks associated with vaccinations pose challenges to immunization requirements. Some states offer not only medical and religious exemptions to immunization requirements, but also philosophical exemptions for parents who choose not to immunize their children. Policy makers must balance the need to provide individual choice with the need to protect children's health.