Starting from the premise that common methods for scoring situational judgment tests (S]Ts) produce measures of procedural knowledge, this chapter develops a theory about its causal antecedents in the form of experiential and dispositional variables and its consequences for job performance. The concept of implicit trait policy (lTP) plays a central role in this theory. ITPs are implicit beliefs about the effectiveness of different levels of trait expression. The theory explains relations between personality scores and SJT scores by arguing that ITPs mediate relations between personality traits and procedural knowledge. Experiential variables in the theory are presumed to have causal effects on both ITPs and procedural knowledge. This chapter reviews empirical studies that test theoretical predictions that individuals' personality traits are correlated with their ITPs and that ITPs mediate effects of personality traits on procedural knowledge.