Although research acknowledges the role of IS in a merger, it has not addressed the issue of boundary management during the development of ISs aimed at supporting merged organizations. Yet, it has been shown, albeit not in a merger context, that knowledge sharing during IS development involving agents from different communities is critical and difficult. Hence, our study addresses the questions of how agents from merging organizations, engaged in an IS development during post-merger integration (PMI) share knowledge of the work practices required by a specific PMI approach, and of how the resulting IS functionalities are affected by, or do affect the implementation of a PMI approach? Adopting a practice perspective, we aim at developing a theory on knowledge sharing in this context. To do so, we conduct a case study of three IS developments within a merger in the healthcare milieu.