Niklas Luhmann was one of the most innovative and productive social theorists of the 20thcentury. He developed a comprehensive and distinctive social theory and his ideas have enrichedmany disciplines. Yet, only few geographers have engaged with his work. Convinced of its qualities,our intention is to stimulate a critical reception of his theory among human geographers. Herean introduction into his theory of social systems is provided, and the possibilities for a geographyof social systems is explored. A key element of our proposal is a differential notion of space as apossibility of distinction, which complements Luhmann's epistemological notion of time. Our conclu-sion is that a geography of social systems would have to set out conceptually from accessibilitysystems, which are systems that encompass communications, their necessary physical and ecologicalenvironment, as well as their coordination in various dimensions of space and time