The present study integrates the literature on social loafing and organizational citizenship behavior (OCB). The authors examined the roles of personality, motives, and contextual factors in influencing the work behaviors of OCB and social loafing. In a sample of 341 individuals working in project groups, with data collected over 3 time periods, the authors found that conscientiousness was negatively related to social loafing. They also found the known positive relation of OCB with conscientiousness. Felt responsibility was negatively related to social loafing. The authors found no significant relations between social loafing and OCB motives.