The goal of the current project was to determine (a) the cognitive abilities assessed by the Mini Mental State Examination (MMSE; M. F. Folstein, S. E. Folstein, & P. R. McHugh, 1975), (b) whether the same abilities are associated with MMSE performance among people of different ages, and (c) whether the same abilities are involved in changes within the same people over time. The authors therefore examined whether the initial levels of 5 cognitive ability constructs (vocabulary, reasoning, memory, space, and speed) predicted initial levels of MMSE performance and whether the initial levels or the changes in these 5 cognitive abilities predicted change in the MMSE performance. The major findings were that 3 cognitive constructs (vocabulary, reasoning, and memory) contribute to performance in the MMSE but that their respective contributions to the MMSE vary as a function of age and time. In particular, individual differences and change in the MMSE are primarily related to individual differences in reasoning among adults younger than about 70 years, whereas both initial level of MMSE performance and longitudinal change in MMSE performance primarily related to initial level and change in memory ability among adults older than 70 years. The results therefore imply that both the level of performance on the MMSE at a single point in time and the change in MMSE over time may represent somewhat different cognitive abilities at different ages. (Contains 1 footnote, 4 tables, and 1 figure.)