Abstract Understanding trends in dementia incidence, prevalence, and associated risk factors, is critical to improving our understanding of the burden of the disease and for public health efforts and individual interventions focusing on hitherto identified and potentially modifiable lifestyle factors. Over the last years, an increasing number of studies have suggested that the incidence of dementia has been decreasing over the past two decades. However, few epidemiological studies evaluated the role of birth cohort on cognitive impairment later in life and there are some conflicting results. Moreover, attempts have been made to understand which factors may underlie such changes, but findings are thus far inconclusive. Differences in environmental exposures, lifestyle factors, and patterns in chronic disease across birth cohort might explain observed changes in patterns of cognitive aging. Cohort effects, defined by birth year, result from differences in exposures and develop through different historical periods. There is potential for interactions among age, cohort, and period effects and these too must be considered in understanding changing trends in cognitive dysfunction. A number of questions remain unanswered and will be addressed by this project: Are there differences in educational attainment, lifestyle and health behaviors, socioeconomic conditions, and cardiovascular burden in later born generations relative to earlier birth cohorts? Do these cohort differences explain the cohort differences observed in cognitive trajectories and incidence of cognitive impairment? Do these risk factors interact within and across cohorts that might further explain cohort differences in cognitive change and impairment? Can we identify differences between women and men?