The emergency nurse practitioner (ENP) is a rapidly developing role within emergency health care provision in the United Kingdom (UK). This paper explores some of the available literature concerning the development of the role in the context of major accident and emergency departments. The professional and legal implications of this shift in role boundaries are discussed. The current inconsistencies in educational provision and the potential consequences for practice in this area, are highlighted. The relative plethora of rigorous evaluation studies of ENP role effectiveness in North America, is contrasted with the current paucity of empirical data available in the UK. A number of methodological issues concerning the evaluation of ENP services are identified. The need for research in this area, alongside a programme of continuing local audit to guide and inform evidence-based practice, is emphasized.