This paper aims at developing a framework for business-to-business (B2B) inter-organizational systems (IOSs), based on real-world IOS examples. Based upon two dimensions, role linkage and system support level, we propose a new framework that classifies IOSs into four basic types: (1) resource pooling, (2) operational cooperation, (3) operational coordination, and (4) complementary cooperation. We review select cases that fit into each category and consider the common characteristics of systems in each category. Then we draw implications for IOS planning and suggest a five-step process for creating an IOS plan. It is argued that each category of IOS needs to be linked with a specific business strategy, although each employs a common technical infrastructure.