It has been reported that the outcomes of care are affected not only by the educational preparation and experience of the practitioner but also by the parameters of his or her practice. Given differences that exist internationally in the enactment of the emergency nurse practitioner (ENP) role, a synthesis of research articles was conducted to examine the educational preparation and experience of ENPs, the role(s) they assume as determined by their patient population, and the outcomes used to evaluate their practice. The synthesis was informed by Sidani and Irvine's (1999) conceptual framework for evaluating the nurse practitioner role in acute care settings. The synthesis included 43 research articles, which were retrieved following a search of the Cumulative Index to Nursing and Allied Health Literature (CINAHL) bibliographic database. Approximately 60% of the articles were descriptive or qualitative studies, whereas only 7% were randomized controlled trials. Findings suggest that although many outcomes of care have been evaluated, no outcomes have been evaluated consistently and many are not specific to the intervention or actions of nurse practitioners. In addition, few research articles provide information on the educational preparation and experience of the ENPs or the parameters of their practice. Such information is needed to explain the variability observed in the outcomes achieved and to build a body of evidence supporting the role of nurse practitioners in the emergency department.