To support rehabilitation health care professionals' efforts to increase physical activity levels among their outpatient rehabilitation and postdischarge patients, we review the Exercise is Medicine (EIM) initiative. The EIM initiative was launched in 2007 jointly by the American College of Sports Medicine and American Medical Association. Three principles underlie the EIM initiative. First, physical activity should be monitored as a vital sign; second, physical activity is an effective medical modality and should be prescribed; and third, success of their vision requires top down and bottom up efforts by 3 key stakeholder groups: health care providers, exercise professionals, and the community. The target weekly physical activity level is 150 minutes of moderate-to-vigorous physical activity, as established by the Centers for Disease Control and Prevention and World Health Organization. Persons falling below the weekly target physical activity level should be prescribed physical activity and/or referred to an exercise professional for implementation support. Selection of an exercise professional for referral is based on the patient's risk stratification and need to participate in clinically supervised physical activity.