All states offer medical exemptions to school immunization requirements, and 48 states offer non-medical exemptions. Prior research has shown that easily granting non-medical exemptions has been associated with higher exemption rates, increasing exemption rates, and incidence of pertussis. Several states with historically high rates of exemptions have recently added restrictions to their exemption policies in an effort to reduce the frequency of exemptions and more effectively control disease. This project aims to explore the implementation of changes to exemption laws, evaluate the impact of these changes, and develop a model nonmedical exemption law. The project will focus on the four states that have recently added restrictions to their exemption laws: California, Oregon, Vermont, and Washington. The team will conduct in-depth interviews with state and local immunization program personnel and school officials to assess how changes to the law were implemented, and will examine statewide and local exemption rates to assess the impact of the changes on the laws on exemption rates and the clustering of exemptions.