Building on social identity theory, we theorize and find that in a merger, paired family firms are better able to retain employees and improve postmerger performance compared to other merger pairs. We contribute to social identity theory by theorizing better postmerger performance as mediated by job security for family firm combinations. We also contribute to the job security and M&A literature by examining how job security and postmerger performance vary based on the paired social identity of owners. In addition to identity similarity, the type of identity also matters in mergers. We argue that family owner social identity similarity fosters greater integration between merging parties while allowing family owner pairs to retain some autonomy through their employees, thereby maximizing postmerger performance. Our data on private Swedish firms, complemented by eleven qualitative interviews across five countries and three continents, confirm that family mergers outperform other merger combinations via job security. In a supplementary critical experiment examining industry dissimilarity, we compare the socioemotional wealth perspective–which emphasizes loss aversion and predicts family firms’ unrelated diversification avoidance–to the social identity theory. Consistent with social identity theory, our results show that both job security and postmerger performance improve with unrelated family firm mergers.