This study examined two hypotheses regarding the moderating effects of job characteristics on the validity of personality. Using meta-analytic techniques, the authors explored the extent to which the structural characteristics and cognitive ability requirements of jobs influence the role of conscientiousness in predicting performance. The results suggest that conscientiousness is a stronger predictor of performance in jobs that are highly routinized, and a weaker predictor of performance in jobs with high levels of cognitive ability requirements. Implications for theory and future research are discussed.