This paper considers the nature of the concept of an information system and particularly its basis as a socio-technical system. We argue that while socio-technical ideas have been heavily used within the discipline of Information Systems, the way in which an information system itself is socio-technical is quite poorly explained in such literature. We seek to address this by using a conceptual framework founded in organizational semiotics and systemics which directly locates an information system as mediating between activity systems on the one hand and technology systems on the other. We ground our discussion in a range of examples from different historical periods and cultures. This helps us demonstrate some of the universal features of information systems, whilst also demonstrating the central place of information systems in the sociomaterial practices of organizations.