In this study, we examine how firm-specific client capital impacts firm performance, new business generation for clients, and employee mobility. Extant studies in both strategic management and strategic human capital have noted the importance of firm-specificity relating to resources and human capital. What is largely understudied, however, is the knowledge about the firm-specific supplier-client relationship; what we refer to here as firm-specific client capital. In studying firm- specific client capital, this study purports to understand how firm-specific client capital impacts organizational-level outcomes, and how knowledge integration practice moderates these relationships. To do so, we draw our theory based on the resource-based view of the firm, relational view, transaction cost economics, and the human capital theory to develop a theory regarding the firm-specificity of client capital.