Evaluation of overlap among correlational construct families provides a basis for cross-fertilization in each of the four separate individual-differences domains. This article provides some new insights on Thorndike’s claim that superiority in one trait implies superiority in other traits. Definitions and methodological differences among correlational domains of inquiry are reviewed from modern investigations of personality, self-concept, interests, and intelligence. Sources of overlap between personality and other trait families are discussed and four trait complexes are reviewed: social, clerical/conventional, science/math, and intellectual/cultural. Implications of the trait-complex approach and challenges to integrative research approaches to applied problems are presented.