In the current article, we provide a critical review of the extant literature that has focused on environmental influences on cognitive and brain plasticity over the adult life span. The review includes both human epidemiological, and human and nonhuman cross-sectional and longitudinal research. We review a number of factors that have been suggested to reduce age-related cognitive decline including both formal and informal education, leisure pursuits, intellectual engagement, and expertise in different skill domains. We also examine the literature on cognitive and physical fitness training. We conclude with a discussion of the gaps in the literature and suggestions for future research.