Cognitive behavioral therapy for insomnia (CBT-I) is an empirically supported intervention for insomnia. Given the strong, consistent support of its efficacy, scholars have become increasingly interested in the behavioral and cognitive mechanisms targeted during CBT-I. The purpose of the systematic review was to synthesize findings from the literature regarding the associations among maladaptive sleep beliefs, a cognitive mechanism implicated in maintaining insomnia, and treatment outcomes following CBT-I. The systematic review was completed using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Seventeen studies were included in the final sample of reviewed articles and a study quality assessment was performed for all studies included in the review. The results suggested that reductions in maladaptive sleep beliefs were associated with improved insomnia severity; however, reductions in maladaptive beliefs were not associated with changes in sleep efficiency or other sleep parameters. Moreover, in some cases, improved sleep parameters preceded reductions in maladaptive beliefs. Maladaptive sleep beliefs may be an important target for improving insomnia. Targeting maladaptive sleep beliefs may initiate a trickle-down process that limits the influence of other cognitive and behavioral processes maintaining insomnia. Additional investigation is needed to evaluate the directional relationship between improved insomnia symptoms and reduced maladaptive beliefs.