Increasingly, organizations have been investing heavily in information systems to support greater inter- organizational coordination and cooperation with key business partners. However, the adoption of such IOSs appears to depend not only on the firmís perspective, but also on the complementary perspective of each of these partners. Drawing on three IS theoretical perspectives and three views of competitive advantage, this study first develops a relational perspective which we posit to have general applicability in several different contexts, including adoption, diffusion and success of dyadic IOS implementations. In this current study, the relational perspective is operationalized in the specific context of dyadic IOS adoption, and its applicability is being demonstrated in two parts via case studies in the context of the BookNet and CoreNet projects in Singapore. The insights gained and lessons learned from the experiences of these case-study companies may hold valuable implications for both IS research and practice.