This chapter looks at the impact of health and lifestyle factors on the risk of developing dementia in later life. It provides a brief overview of dementia and its most common causes, and an explanation of the degree to which genetics play a role. It reviews the available evidence regarding the extent to which potentially modifiable risk factors including smoking, obesity, physical activity, cognitive activity, diet, alcohol, depression, and diabetes may contribute to a likelihood of developing dementia in later life. Both general dietary patterns and the evidence related to vitamin B12, folate, antioxidants, and omega 3 fatty acids are reviewed. Possible approaches to the conversion of this knowledge into a reduction in the prevalence of dementia in the future are discussed. It is written for anyone with an interest in dementia and potential opportunities to mitigate the impact on individuals and society.