The proposed research will investigate short-term longitudinal change in a broad variety of cognitive variables, with particular emphasis on adults under the age of 60. Although previous studies have found little or no cognitive change in longitudinal comparisons involving young and middle-aged adults, this research will employ two methodological innovations, variable retest intervals and measurement bursts at each occasion, that will allow age effects to be distinguished from retest effects, and will increase sensitivity in the detection of change by taking into account normal short-term variability in performance. Among the primary questions to be investigated are whether age-related cognitive change begins early in adulthood, whether the changes in different cognitive variables are independent of one another and equally so at different periods in adulthood, and the degree to which factors such as one's cognitive or physical lifestyle moderate the amount of age change in different cognitive abilities at various periods in adulthood. Over 700 adults between 18 and 89 years of age who completed the same battery of 13 cognitive tests in 2001, 2002, and 2003 will be invited to participate in the project, as will two new samples of 300 adults each. Most of the participants will be assessed with a measurement burst design of three sessions within a period of about two weeks in either the first or second year of the project, and again in the either the third, fourth, or fifth year of the project. Mixed effects models will be used to obtain estimates of the age and retest components of change for each participant, and these estimates will be examined in terms of their correlations with one another, and with various individual difference characteristics.