This paper examines the concepts of Information System (IS) central to the IS discipline with the aim to contribute to the debate on the nature of the concept and stimulate broader engagement of the IS community. To achieve this aim the paper identifies and critically examines common place conceptions of IS in the literature and also those most explicitly and clearly presented in IS textbooks.. IS are commonly seen as devices that represent reality by collecting and processing data and thereby producing information. Such a model of IS as an ?input-processing-output? device that represents reality is grounded in a representational philosophy. Based on a critical assessment of the representational view of information and IS the paper puts forward an alternative performative view founded on agential realism (Barad, 2007). According to this view any observation of the world is mediated by devices, that is, grounded in particular interactions with and translations of the world through devices, which therefore form an integrative part of observed phenomena. Following the performative view, the paper proposes and articulates a new concept of IS as 'apparatus' defined as sociotechnical entanglement of IT artifact, work practices, users, and developers. Theoretical and practical implications of understanding IS as apparatuses are discussed.