Traditional approaches to understanding individual differences determinants of domain-specific expertise have focused on individual trait components, such as ability or topic interest. In contrast, trait complex approaches consider whether combinations of cognitive, affective, and conative traits are particularly facilitative or impeding of the development of domain knowledge. This article reviews an investment theory and empirical research concerning a relatively small set of trait complexes that appear to be instrumental correlates of both individual and group differences in expertise across several academic domains. Implications for academic counseling and instructional interventions are discussed. (Contains 2 figures.)