AbstractIn this chapter the domain of relationship management (RM) is discussed and the notion of the RM mid-range theory is introduced. The first section highlights the socio-economic duality of RM and presents the core characteristics of the RM business model. The diversity of partly overlapping relational constructs is commented on, and a uniform semantic programme for RM is proposed that links the notion of relationship capital and three RM dimensions: structural, psychological and behavioral. In the second section, the role of mid-range theories in linking macro and micro theoretical levels is presented. The theoretical boundaries (the content) of the envisioned RM mid-range theory are outlined, which link the RM business model, the key relational activities and approaches, and business performance. A hypothetical system of theories for competitive advantage is drafted, where the general theory level is occupied by the Resource-Advantage Theory of Competition followed by the upper mid-range theory level; where the RM mid-range theory is placed, completed by the specific market type mid-range theory level; and where network-based and market-based relational theories are positioned.