Software systems are subject to increasing complexity and in need of efficient structuring. Multi-agent system research has come up with approaches for an organization-oriented comprehension of software systems. However, when it comes to the collective level of organizational analysis, multi-agent system technology lacks clear development concepts. To overcome this problem while preserving the earnings of the agent-oriented approach, this paper propagates a shift in perspective from the individual agent to the organization as the core metaphor of software engineering targeting at very large systems. According to different levels of analysis drawn from organization theory, different types of organizational units are incorporated into a reference architecture for organization-oriented software systems. Categories and Subject Descriptors D.2 [Software Engineering]: Architectures; J.4 [Social and Behavioral Sciences]: Sociology; K.6 [Management of Computing and Information Systems]: Softw...