Implementing large strategic IS in the UK health sector has recently become the subject of much debate, as hospitals have undergone wide-reaching government-led institutional reforms involving the introduction of IT. Many of the developments have followed the patterns in the U.S. One such example is that of Case Mix, introduced strategically as part of the Resource Management Initiative and aimed at the facilitation of both clinical and financial audit. Moreover, Case Mix was implemented alongside significant changes in hospital structure and culture, requiring clinicians to get involved in management tasks and decision making within the structure of the hospital, supported by a new information infrastructure. Case Mix was implemented blanket-fashion throughout many UK hospitals, and the success of such systems has varied significantly. A number of lessons can be learned from the way that the implementation was approached. This chapter stems from a research project focusing longitudinally on the implementation of Case Mix in four UK hospitals. It draws a number of findings from the cases, and importantly, explicates a framework for strategic IS implementation, as generated from the cases and supported by the extant literature. Such a framework has implications for both theory and practice, and assists in the understanding of what is often a dynamic and poorly understood situation.