Stroke is a major cause of death and disability in the world. The main causes of stroke are atherothromboembolism and cardiogenic embolism. The main causal and treatable risk factors for atherothromboembolic ischemic stroke are increasing blood pressure (BP), increasing cholesterol, cigarette smoking and diabetes; and the main risk factors for cardiogenic ischemic stroke are atrial fibrillation (AF) and ischemic heart disease. Strategies to reduce the incidence of stroke include prevention of first-ever and recurrent stroke, and treatment of patients with acute stroke to reduce death and disability. The two main strategies of stroke prevention are the 'population' (or 'mass') approach and the 'high risk' approach. The 'population' approach aims to reduce stroke by lowering the prevalence and mean level of causal risk factors in the community, by means of public education and government legislation. The 'high risk' approach aims to reduce stroke by identifying individuals at high risk of stroke, and lowering their risk by means of optimal medical therapies. Level I evidence from randomized controlled trials indicates that effective treatments for high risk patients include control of causal risk factors (lowering BP, lowering blood cholesterol), antithrombotic therapy (antiplatelet therapy with aspirin, clopidogrel, or the combination of aspirin and dipyridamole for patients in sinus rhythm, and anticoagulation with warfarin or ximelagatran for patients in AF) and, where appropriate, carotid revascularization for patients with severe carotid stenosis.