Purpose: To understand the boundary dynamics between organizational and individual identities that are negotiated in mergers. Originality/value: This was the first study to explore the interface of the boundaries between individual and organizational identities in merger contexts. Design/methodology/approach: The results are presented as a grounded theory based on interviews with 64 individuals from 16 different companies that have undergone mergers. Findings: We analyzed conflict, intrusion, distance and balance as consequences of internal and external identity boundaries’ (in) congruence between organizations and discussed how companies can minimize individual and organizational (of the merged company) identity conflicts through boundary work. Furthermore, we discussed the relationships between organizational and individual identity boundaries. The grounded theory we developed held that the degree of permeability between the internal and external boundaries between the organizations involved in a merger determines the types of episodic events and permanent states of conflict between organizational identities. In general, our study contributes to a holistic and comprehensive vision of how the boundaries between identities at the organizational and individual levels contribute to identity formation and the retention of individuals in the new merged organization. Suggestions for practice and for future researches are provided.