This report reviews a theoretically inspired empirical investigation of individual differences in knowledge, abilities, and nonability traits as part of an ongoing effort to better understand adult intellectual development and to develop more accurate measures of adult intelligence. Twenty Knowledge Scales were constructed, drawing on College-Level Examination Program® (CLEP®) and Advanced Placement Program® (AP®) Examinations. These Knowledge Structures were administered, along with an extensive battery of traditional ability tests, and measures of personality, interests, and self-concept, to two samples of adults, a "younger" adult group, age 18-27, and an "older" adult group, age 30+. Results indicate that the older adults in this sample know a lot more than the younger adults across a broad range of domains that are represented both inside and outside of standard college curricula. In general, the older adult group showed a much higher degree of orientation toward things "intellectual" than the younger adult group, as indicated by scores on interest, personality, and self-concept scales. The following is appended: Six Selected Case Profiles. [This report was written in collaboration with Eric L. Rolfhus.]