In 2 field studies (Ns = 71 and 113), we tested the prediction that in-group identification would mediate the acquisition of group norms by new group members. Study 1 demonstrated that participants surveyed after a team-development program reported greater awareness of in-group norms of teamwork and cooperation, compared to those surveyed at the start. Moreover, there was evidence that this effect was mediated by increased in-group identification. Study 2 replicated this finding, and showed that the effects were specific to the norm of teamwork. Acquisition of alternative norms of individualism and competitiveness did not increase after participation in the program, and did not correlate with identification. Practical implications and future work are discussed.