The paper critiques a case study of the use of a customer relationship management system in a telecommunication company. Based on published quotations from the field study, some core concepts concerning the behaviour of information systems in organisations are developed. Discussion of the CRM implementation leads to the proposal of a definition of an information system as: An information system mediates a relationship towards an agreed outcome or purpose; To do this objects-of-interest are manipulated through processes, Conforming to a negotiated interpretation of the real world. Analysis of the case study leads to the identification of 38 concepts and the definition of a set of core concepts: purpose, objectification, legitimisation, selection-exclusion, primacy of the model and behaviour change. The gap between the information systems model and the realty of the organisation is discussed.