Cooperating When “You” and “I” Are Treated Fairly: The Moderating Role of Leader Prototypicality David De Cremer and Marius van Dijke Erasmus University Rotterdam David M. Mayer University of Michigan We developed a model predicting that leaders are most effective in stimulating follower cooperation when they consistently treat all group members in a fair manner and are prototypical (i.e., representative of the group’s values and norms). In support of this idea, we consistently found that group members cooperated most when prototypical leaders treated themselves as well as their coworkers fairly across a laboratory experiment and 3 cross-sectional field studies. These findings highlight the important role of others’ fairness experiences and perceptions in influencing one’s own reactions and also the role of leaders as representing the group’s values and norms. We discuss implications for fairness theory and the leader prototypicality literature. Keywords: procedural fairness, others’ procedural fairness, OCB, cooperation, prototypicality It is often crucial for the effective functioning of teams, work- groups, and organizations that members are willing to engage in behaviors that are beneficial to the collective, rather than focusing solely on their own benefits (Derlaga & Grzelak, 1982; Smith, Carroll, & Ashford, 1995). Hence, promoting cooperation among group members is considered a core function of leadership (Hogan, Curphy, & Hogan, 1994). In the present research, we operation- alize cooperation as being related to helping behavior, promoting the collective interest, and organizational citizenship behavior (OCB; cf. Derlaga & Grzelak, 1982; Podsakoff, Ahearne, & MacKenzie, 1997). An effective way for leaders to promote cooperation is by enacting procedures in a fair manner (for meta-analyses, see Cohen-Charash & Spector, 2001; Colquitt, 2001). This is because procedural fairness indicates that individuals are valued and re- spected members of a group that they can be proud of, which contributes positively to their group identity (De Cremer & Tyler, 2005; Tyler, 1999). This positive group identity consequently improves cooperation (Blader & Tyler, 2009). However, a limita- tion of this research and of the overwhelming majority of proce- dural fairness studies is that scholars have typically focused on how people’s personal procedural fairness experiences motivate cooperative behavior (for a recent overview, see Blader & Tyler, 2009). Extending prior work, we propose that examining the impact of procedural fairness on cooperation within social settings implies that the fairness experiences of all actors involved need to be examined. We argue that in a specific context, procedurally fair treatment that group members experience themselves stimulates cooperation, particularly when other group members are also treated procedurally fairly. Consistent with the identity processes that we theorize underlie the interactive effect of procedurally fair treatment for self and others on cooperation, we also study the role of whether the leader is considered legitimate to communicate group identity-related information, such as fair treatment. Building on the social identity analysis of leadership (Hogg & van Knippenberg, 2003), we advance the hypothesis that leader prototypicality, which refers to the leader being representative of the group’s identity and values, is one such leadership type (D. van Knippenberg & Hogg, 2003). Specifically, we test whether the positive interactive effect of procedural fairness for oneself and for fellow group members on cooperation is pronounced when the enacting leader is prototypical of the group. We believe that investigating this three-way interaction effect on cooperation is important for three reasons. First, this re- search extends the traditional “first person” emphasis of pro- cedural fairness research and moves toward a more social dynamic approach by exploring the effects of one’s own and others’ treatment on one’s willingness to cooperate toward the group’s goals. Second, we identify a theoretically relevant moderator variable related to the enacting leader (prototypical- ity) that is in line with the proposed identity process underlying the Procedural Fairness Self  Procedural Fairness Others interaction. As such, we highlight when and, thus, why a social dynamic approach of procedural fairness is most likely to explain group member cooperation. Third, these studies allow us to integrate two independent research traditions on proce- dural fairness and leadership. This approach responds to D. van Knippenberg, De Cremer, and van Knippenberg’s (2007, p. 129) comment that “remarkably little research has been done on the interactive effects of leader fairness and other aspects of leadership . . . and here potentially lies the greatest challenge for research in leadership and fairness.” This article was published Online First August 30, 2010. David De Cremer and Marius van Dijke, Rotterdam School of Manage- ment, Erasmus University Rotterdam, Rotterdam, the Netherlands; David M. Mayer, Department of Management and Organizations, Stephen M. Ross School of Business, University of Michigan. Correspondence concerning this article should be addressed to David De Cremer, Rotterdam School of Management, Erasmus Centre of Behav- ioural Ethics, Erasmus University Rotterdam, P.O. Box 1738, 3000DR Rotterdam, the Netherlands. E-mail: ddecremer@rsm.nl Journal of Applied Psychology © 2010 American Psychological Association 2010, Vol. 95, No. 6, 1121–1133 0021-9010/10/$12.00 DOI: 10.1037/a0020419 1121