Background: Despite well-articulated benefits, the introduction of Nurse Practitioners (NPs) in Australia has been slow. Poorly defined nomenclature relating to advanced practice roles in nursing and variations in such roles both across Australia and worldwide have resulted in confusion and uncertainty regarding the functions and roles of NPs. Qualitative studies focussing on the perceived impact on the care settings into which NPs are introduced are scarce, but are valuable in providing a complete contextual account of NPs in care delivery settings. This study aimed to investigate the perceived impact of the NP on the delivery of care in the ED by senior doctors, nurses, and NPs. Results will facilitate adoption and best use of this human resource innovation. Methods. A cross-sectional qualitative study was undertaken in the Emergency Departments (EDs) of two large Australian metropolitan public teaching hospitals. Semi-structured, in-depth interviews were conducted with five nurse practitioners, four senior doctors (staff specialists and ED directors) and five senior nurses. Transcribed interviews were analysed using a grounded theory approach to develop themes in relation to the conceptualisation of the impact of the NP role on the ED. Member checking of results was conducted by revisiting the sites to clarify findings with participants and further explore emergent themes. Results: The impact of the NP role was perceived differently by different groups of participants. Whilst NPs were observed to deliver few quantitative improvements to ED functioning from the perspective of ED directors, NPs believed that they assisted doctors in managing the increasing subacute presentations to the contemporary ED. NPs also believed they embraced a preventative paradigm of care which addressed the long term priorities of chronic disease prevention and cost containment in the broader healthcare environment. The ambiguous position of the NP role, which crosses the gap between nursing and medicine, emerged and resulted in a duality of NP governance. Conclusions: Interpretation of the NPs' role occurred through different frames of reference. This has implications for the development of the NP role in the ED. Collaboration and dialogue between various stakeholders, such as ED doctors and senior nursing management is required.