In this systematic review, we synthesize the literature on the relationship between retirement and cognitive functioning and highlight dimensions of heterogeneity in the findings. Most studies find no effect or a negative effect of retirement on cognitive functioning and risk of cognitive impairment. Heterogeneity in the relationship is observed, most notably by sex and occupation, though differences also exist by education level and country context. A few studies find a positive effect of retirement on cognition among individuals employed in manual labor or skilled trades. We conclude our review by describing data infrastructure improvements and future research opportunities.