Medicaid is the largest health insurance program in the United States, covering more than 76 million individuals. Federal Medicaid requirements set broad standards for the benefits and populations states must cover, but modifications through state plan amendments and waivers allow individual states to adjust the Medicaid program to fit their residents’ needs. State plan amendments and waivers address different aspects of the Medicaid program and therefore have unique requirements and approval processes. This issue brief outlines these two mechanisms for changing payment and delivery system models in state Medicaid programs and presents descriptions and notable uses for five types of Medicaid waivers.