Firms manage numerous inter-organizational relationships. Key account management (KAM) is a concept used to manage a specific subset of these relationships, i.e. a supplier firm's relationships with strategically important customers. Scholars have studied different elements of KAM such as actors, resources, or relationships. Surprisingly few studies discuss the link between KAM and competitive advantage. By adopting a capability perspective on KAM, we seek to develop a theoretical basis to better explain its performance-implications. The capability perspective is compatible with extant approaches and complements them with new arguments concerning the value that a KAM system has in competition. The purpose of our article is to develop a conceptual model of a supplier firm's KAM capability and to indicate avenues for future research.