The purpose of this research is to identify the effectiveness of primary care-based interventions designed to increase older adults' physical activity (PA). Primary care was defined as a patient's main source of health care. Standardized mean difference effect size (ES) was calculated related to changes in PA levels in adults' ≥65. Moderator analysis was performed to explore the relationship between participant characteristics, interventions, interventionists, and ES. Overall mean ES 0.27 (95% confidence interval [0.15, 0.39], p < .01) was calculated for 25 two-group comparisons involving 4,685 total participants with a mean age of 75.08. There was little evidence to support counseling over exercise referrals. The use of theory or a pedometer did not modify the ES. PA interventions delivered in primary care are effective and can be delivered by other health-care providers working with the primary provider. Many different behavior change strategies may be used to promote PA.