The incidence and prevalence of dementia are expected to increase several-fold in the coming decades. Given that the current pharmaceutical treatment of dementia can only modestly improve symptoms, risk factor modification remains the cornerstone for dementia prevention. Some of the most promising strategies for the prevention of dementia include vascular risk factor control, cognitive activity, physical activity, social engagement, diet, and recognition of depression. In observational studies, vascular risk factors—including diabetes, hypertension, dyslipidemia, and obesity—are fairly consistently associated with increased risk of dementia. In addition, people with depression are at high risk for cognitive impairment. Population studies have reported that intake of antioxidants or polyunsaturated fatty acids may be associated with a reduced incidence of dementia, and it has been reported that people who are cognitively, socially, and physically active have a reduced risk of cognitive impairment. However, results from randomized trials of risk factor modification have been mixed. Most promising, interventions of cognitive and physical activity improve cognitive performance and slow cognitive decline. Future studies should continue to examine the implication of risk factor modification in controlled trials, with particular focus on whether several simultaneous interventions may have additive or multiplicative effects.