Thematic analysis of data from nine exploratory focus groups conducted with 71 middle-aged and older African American men and eight focus groups with 77 key women in their lives revealed how social norms and modeling of physical activity influenced men's motivation to exercise. Both men and women identified male peers as an important source of ideas, encouragement, and support to initiate and sustain physical activity, yet sedentary peers also could contribute to men being less motivated to be active. The primary difference in men's and women's perspectives was that men attributed their decline in activity levels to difficulties in finding time for physical activity, whereas women attributed sedentary lifestyles to an increase in men's physical illnesses and ailments. Men's participation in team sports and overall activity levels diminished with age. Peer social support can be critical for interventions to help African American men engage in and sustain physical activity.