The idea of cognitive reserve stems from the repeated observation that there does not appear to be a direct relationship between the degree of brain pathology or brain damage and the clinical manifestation of that damage. Cognitive reserve may be based on more efficient utilization of brain networks or of enhanced ability to recruit alternate brain networks as needed. A model for the study of cognitive reserve will be developed. Epidemiologic evidence that support this concept of cognitive reserve, and functional imaging studies that explore the neural mechanisms underlying cognitive reserve will be presented.