The concept of reserve has been developed to account for the discontinuity between the extent of brain damage at its clinical manifestation in the form of cognitive decline or dementia. In this chapter, we discuss contributors to cognitive reserve from various stages of the life-course, including childhood, early adulthood, middle age, and late life. Evidence from observational studies as well as intervention trials is presented and assessed. We conclude by arguing that reserve formation in dementia risk is a life-course process whereby baseline cognitive abilities are subjected to modulation by subsequent experiences at diverse stages over the entire life-course. Variations among individuals in their ability to withstand age-related brain changes are ultimately dependent on their life-time accumulation of mental, physical, and lifestyle inputs into cognitive reserve.