Cognitive decline is a common feature of aging. Physical activity is a modifiable lifestyle factor that has been identified as positively impacting cognitive health of older adults. Here, we review the current evidence from epidemiological (i.e., longitudinal cohort) and intervention studies on the role of physical activity and exercise in promoting cognitive health in older adults both with and without cognitive impairment. We highlight some of the potential underlying mechanisms and discuss some of the potential modifying factors, including exercise type and target population, by reviewing recent converging behavioral, neuroimaging, and biomarker evidence linking physical activity with cognitive health. We conclude with limitations and future directions for this rapidly expanding line of research.