Bridging Systems Theory and Information Systems: A Framework for Designing Complex Information Systems Information Systems (IS) is rooted in systems theory. Systems theory offers powerful concepts to address challenges of growing system complexity and non-systemic design approaches in information systems. Despite its systemic origins, systems theory remains a peripheral topic in IS. The study addresses this gap by introducing a comprehensive framework of 52 systems-theoretical concepts to guide the design of complex IS artifacts. We synthesize scattered systems knowledge from diverse disciplines to provide a unified level of abstraction for complex information system design. We apply the framework to a use case of business reputation systems to show how the systems lens informs the design of a novel, complex information system. We make three key contributions to the literature. First, the framework provides a common ground for interdisciplinary research in information system design. Second, it offers a unified level of abstraction grounded in systems theory that serves as a coherent basis for artifact design. Third, it demonstrates the potential of systems theory as a foundational justificatory knowledge base. Furthermore, we provide guidance on applying the framework across multiple modes of reasoning, alongside further application guidelines. The study thus serves as a bridge between the body of systems knowledge and contextual design in IS. AIS