In an interorganizational relationships (IOR) context, interorganizational information systems (IOS) need to be integrated in order to support collaboration between partners and provide a fuller exploitation of the systems they share. Although research stresses the importance of the two phases of the IOS integration, that is the systems development and the systems diffusion, there is a paucity of studies on the mechanisms underlying the integration process and their recursive relationships. Adopting a processual approach and drawing on the concept of social mechanisms, we propose a multilevel conceptual framework that conjectures about the dimensions of the IOS integration process and the underlying social mechanisms that explain the how of the process and the relationships that dynamically link these dimensions. Keywords Interorganizational information systems, IOS integration process, social mechanisms, deep structures, surface structures.