In this paper, we report on MAORI, a Model-based Architecture for ORganizational Interoperability between agents and open MASs that were designed and implemented with heterogeneous organizational models/infrastructures. MAORI is structured along three layers: the Organizational Metamodels (OMM), the Model Transformations (M2M) and the Organizational Interoperability (ORI) layers. Building upon previous work, we focus on the rationale, design and implementation of the ORI layer.