This report investigates arguments that justify state preemption of local lawmaking on the basis that local laws produce a harmful “patchwork” of regulations within a state. We examine the use and merits of the patchwork argument across 10 policy areas, (focusing on paid sick leave, rent control, plastic bag bans and regulations, and antidiscrimination laws) and review the evidence around the patchwork argument’s merits. We find little research evidence that a patchwork of local laws harms businesses, residents, or consumers. Arguments in favor of preemption generally focus on the supposed harm of the regulation itself, rather than on the marginal costs of a patchwork of local laws. Given this lack of evidence, we recommend more research studying the marginal costs and benefits of having different local laws in different jurisdictions.