Relationship marketing effectiveness at improving a firm’s financial performance varies widely, which suggests a need understand better how relationship marketing works and what determines its efficacy. Theory and empirical results from multiple studies will be discussed that provide insight into relationship marketing’s effectiveness. The first study demonstrates that gratitude plays an important role in understanding how relationship marketing investments increase purchase intentions, sales growth, and share of wallet. The project identifies a set of managerially relevant factors that alter customer gratitude, which can make relationship marketing programs more effective. The second study integrates social network and exchange theory to develop a model of customer value based on three relational drivers: relationship quality, contact density, and contact authority. The results suggest the value generated from interfirm relationships derives not only from the quality of customer ties (e.g., trust, commitment, norms), as typically modeled, but also from the number and decision-making capability of interfirm contacts and the interactions among relational drivers. Moderator analysis of customer characteristics suggests that increasing contact density most benefits sellers with customers with high employee turnover rates, whereas building relationships with key decisions makers generates the highest returns among customers that are more difficult to access. The final study investigates the role of relationship velocity—or the rate of change in relational constructs with respect to time—in driving exchange outcomes, using to longitudinal data from more than 400 business-to-business relationships. The study findings highlight the importance of tapping into the dynamic nature of relational constructs (e.g., velocity) to provide insights into future sales growth, beyond those captured at the level of relational constructs.