This chapter presents a review of the state of the art on the topic of knowledge transfer following post-merger integration (PMI) in international mergers and acquisitions (M&A) and identifies points of agreement and disagreement, recognizes underexplored areas and provides suggestions on how they could be explored in future studies. The chapter points to the limited amount of literature that describes knowledge transfer following international acquisitions, while highlighting it as an emerging field of research. The knowledge transfer literature mainly refers to innovation and innovation capabilities, while areas such as marketing and customer knowledge are vitally absent in the literature. In any international acquisition, such knowledge transfer would be of fundamental importance, given the acquisition motive to reach new markets or customers. Two case studies on the transfer of knowledge about customers following international acquisitions are provided. The case illustrations point to a focus on knowledge transfer on strategic levels in the post-merger integration following international acquisitions, while the operational sales forces’ transfer of knowledge is largely disregarded in practice. Since much of the tacit knowledge about customers is handled on that level, it needs to be recognized and developed. The chapter indicates that raising the awareness of the transfer of knowledge about customers following international acquisitions is important from a practitioner’s as well as a research point of view.