This article examines within-person consistency in personality expression across situations as an individual difference variable that is distinct from the typically studied personality trait level. The focus of the study is the manner in which personality consistency (a conceptualization of personality strength) influences the choice and interpretation of situations and, ultimately, the enactment of organizational citizenship behavior. We conducted an experience sampling study of 167 employees over 10 workdays. At each survey, participants reported their conscientiousness, agreeableness, situation perceptions, and organizational citizenship behavior. Results demonstrated that even after controlling for the linear and quadratic effects of personality trait level (and several other variables): (1) personality consistency increased within-person consistency in organizational citizenship behavior across situations and (2) this relationship was partially mediated by perceived consistency of situational strength and trait-relevant situational content. More broadly, the findings show that individual differences in personality are not restricted solely to the personality trait level. Rather, within-person consistency in personality expression across situations is itself an important individual difference: one that possesses appreciable behavioral consequences in the workplace and one that, consequently, is deserving of considerable future research.