The present study examined the viability of incorporating task-contingent units into the study of personality at work, using conscientiousness as an illustrative example. We used experience-sampling data from 123 managers to show that (a) momentary conscientiousness at work is contingent on the difficulty and urgency demands of the tasks people are engaged in, (b) there are significant and stable differences between people in the extent to which their conscientiousness behaviors are contingent on task demands, and (c) individual differences in task-contingent conscientiousness are related to, though distinct from, individual differences in trait conscientiousness. We also provide evidence in relation to (a) need for cognition as a possible antecedent of task-contingent conscientiousness and (b) adaptive performance on a cognitive task as a possible consequence of it. We discuss the theoretical implications of our findings for the cognitive nature of personality and the way in which conscientiousness is expressed at work. Practical implications in relation to the predictive function of personality and applications that focus on behavioral change are also discussed. (Contains 1 footnote and 3 tables.)