Historically, conscientiousness-performance relationships have been modest, suggesting the need to examine theoretically-relevant moderating variables. Based on theory and empirical research suggesting that performance variance is maximally predicted in the presence of person and situation variables, we examined the moderating potential of work effort and psychological climate on the conscientiousness-performance relationship. Data gathered from 139 predominately part-time restaurant employees revealed that conscientiousness predicted performance in the simultaneous presence of high levels of work effort and positive psychological climate. Conversely, conscientiousness had no empirical association with performance when coupled with other combinations (e.g., high-negative; low-positive; low-negative) of work effort and psychological climate. Implications for research, strengths, limitations, and directions for future research are discussed.