Enterprise Resource Planning (ERP) systems dominate the Information Technology (IT) landscape of global companies. Organisations are at different stages in the implementation process ranging from the initial strategic analysis of implementation options, through completed standard implementations and to the sophisticated exploitation of ERP systems using advanced knowledge management, decision support and supply chain management systems. There are also variances in the perspective of managers regarding the strategic potential of ERP systems. We present a maturity model for ERP systems that identifies three key implementation stages. The model is illustrated using case data from 24 organisations in the US and Europe. In stage one, organisations are managing legacy systems and starting the ERP project. In stage two, implementation is complete and the functionality of the ERP system is being exploited across the organisation. In stage three, organisations have normalised the ERP system into the organisation and are engaged in the process of obtaining strategic value from the system by using additional ‘satellite’ systems including knowledge management and supply chain planning. It is shown that the organisations follow an S shaped curve, and that most companies are in the middle stage.