Peer recognition systems are an increasingly popular management control tool through which employees can recognize and thank one another. I examine the effectiveness of these systems in motivating employee helping behavior. My theory and experimental findings suggest that group affiliation is a key moderating factor in determining the motivating influence of peer recognition systems. Specifically, I predict and find that the presence of a peer recognition system has a greater positive effect on in-group versus out-group helping. Results suggest this occurs because peer recognition systems, by formalizing the opportunity for social approval, sensitize employees to preexisting social expectations. I also predict that the incremental benefit of adding rewards to a peer recognition system will be greater for out-group versus in-group helping because the rewards will strengthen the perceived value of recognition among out-group members but simply replace in-group members’ social motivation. Statistical support for this prediction is weak, however. My findings provide insight into when peer recognition systems are effective in motivating helping behavior.