In food packaging, migration is the transfer of chemical substances from packaging materials into food. Examples include plasticizers from PVC films, bisphenol A from epoxy can linings, mineral oils from recycled board, photoinitiators from printed inks, and metals from containers. Because migrated substances can affect safety and taste, regulators set specific migration limits for authorized materials and require testing under standardized time-temperature conditions that simulate real use. Packaging developers choose barrier structures, functional barriers, and compliant materials to keep migration well below legal thresholds throughout shelf life, and they revalidate whenever formulations, suppliers, or processing conditions change.