Since the very early days of computing, information systems were regarded as “man-machine” systems. This definition is of far greater importance to the teaching of information systems as well as to the profession of information systems developers than is often recognised. The majority of teachers, and textbooks, are still caught in the paradigm that information systems development is a technical “art” rather than a field that concerns sociological, rather than technical problems. This chapter argues that the “human” or sociological side of information systems is of such importance that it should be seen as the core of the discipline, and that information systems are best understood when viewed as social systems. Examining the nondeterministic nature of information systems and applying Ashby’s Law of Requisite Variety are helpful to describe and explain these systems as social systems. The paper also refers to current thinking on systems (especially soft systems methodology) and its place in supporting information systems in a constantly changing environment. Finally, the implications of viewing information systems as social systems are discussed with respect to teaching and research, the impact of information systems on organizations, and the shortcomings of current software engineering methodologies.