One important question that has arisen in the course of implementation of the Affordable Care Act (ACA) is the extent to which the states can impose obligations on grandfathered health plans that are not imposed on those plans by the ACA itself. Section 1251 of the ACA defines grandfathered plans as those in which an enrollee was enrolled as of the effective date of the ACA. It imposes on grandfathered plans some of the new ACA requirements (such as coverage of adult children to age 26) or prohibitions (such as the ban on rescissions or lifetime limits), but not others (such as the prohibition on cost-sharing for preventive care or the requirement that plans offer internal and external appeals). Section 1251 does not, however, expressly address the question of whether states can independently impose requirements or prohibitions on grandfathered plans. This entry discusses this issue.