This report analyzes 18 states' experiences implementing policies to limit "crowd out" the substitution of publicly-sponsored health insurance for private coverage. Interviews with governments officials, providers, and advocates reveal that 11 states adopted a relatively aggressive approach to limit crowd out such as waiting periods during which children must be uninsured before being permitted to enroll in SCHIP. Although waiting periods have been criticized as imposing an enrollment barrier, several states include waiting period exceptions that permit families with very expensive coverage or with children with special health care needs to immediately enroll in SCHIP. Monitoring and using application questions to inquire about health insurance status were also commonly used crowd out prevention policies.