[en]Social identity, or group membership, affects economic outcomes. However, this influence may differ according to the nature of the groups involved. Investigating the weakest group cohesion necessary to influence individual behaviors, we undertook three linked ultimatum game experiments involving a minimal categorization process. Three main results are presented here: (i) Belonging to a minimal group affects behaviors; (ii) Men and women differ systematically in the nature of this influence and (iii) The ‘label’ given to a minimal group is in itself not neutral.[/en]