BACKGROUND: The acute care nurse practitioner role is relatively new and not yet clearly defined. Our institution is in the first phase of a role delineation study that includes model development, validity testing, model revision, and dissemination. OBJECTIVES: To identify domains of practice, activities within each domain of practice, and common conceptual strands that cut across each domain, and to synthesize this information into a usable format to guide practice and role development. METHODS: A nonexperimental study design was used, including review of literature, expert consultation, brainstorming, and review of practice. RESULTS: The patient is central to the model. The identified domains of practice include direct comprehensive care, support of systems, education, research, and publication, and professional leadership. The conceptual strands include empowerment, collaboration, and scholarship. A continuum of experience from novice to expert was also identified within each domain. CONCLUSIONS: The development of the model is the first and most important phase in the role-delineation process. We believe that the model is accurate but still in need of testing. Nevertheless, our model can be used to guide institutions and individual practitioners.