The intangible value of information technology (IT) has triggered researchers' and managers' interests in the knowledge-based economy. It has been increasingly emphasized that firms' IT capital is one of the key determinants of business competitiveness and sustainability. IT capital has usually been hidden in the structural capital as an indicator of either IT investment or the operational performance. There are a number of theoretical arguments about the infrastructural role of a firm's IT capital but limited understanding of how this kind of intellectual capital should be managed in a business environment in which complex resources interplay. Applying the complementarity concept, this study highlights the importance of the management of resource complementarity with IT capital in order to deliver sustainable competitiveness. Through multiple case studies of customer relationship management (CRM) systems management in five financial organizations, we analyze the value of customer relationship management systems in relation to the management of complementary resources, including process, structure, capability, and culture. The findings contribute to a better understanding of the management of IT capital and a better application of the complementarity of IT-related resources.