The Maastricht Aging Study (MAAS) was designed to specify the usual and pathological aging of cognitive function. MAAS is devoted to the age-related decline of memory and other cognitive functions in normal people and the factors that may be involved in this process. What determines a decline in memory function? Why do some individuals show a greater decline than others? Over the past years, a host of factors, including biological, medical, psychological and social variables, have been proposed to have an impact on adult cognitive development. MAAS tries to study these factors in an integrative way. This can be achieved only by studying large numbers of normal healthy adults of all ages and by monitoring them for several years.