Context: NP-Physician relationships have been an area of interest for decades. Recently, much of the debate has centered on the primary care physician shortage, NP scope of practice laws, and the expansion of more NPs into primary care. Despite the importance for patient centered care and healthcare costs, no prior study has synthesized existing research related to NP-physician professional relationships in primary care. Objective: Therefore, the aim of this paper was to conduct a systematic review of the literature on models of care that emphasize interprofessional relationships between physicians and NPs in primary care in the United States. Study Design and Analysis: Systematic review - the review methodology followed the PRISMA framework. Setting or Dataset: PubMed, Embase and Cinahl databases and a hand-search of relevant articles. Population studied: The database search aimed to capture the following four concepts: physicians, nurse practitioners, primary care, and interprofessional relations. Inclusion criteria were written in the English language, sufficiently related to the topic, correct population and setting, and a model of care was identifiable. Outcome Measures: After abstract screening and full-text review, data was extracted, synthesized and analyzed based on study design, methods, types of care models described, definition for those models, MD-NP interaction, outcome variables, operationalization and results. Results: 48 studies were included in the systematic review. Expected Outcomes: Across the 48 studies, the authors identified three study design categories, utilizing various types of methods. Different types of models of care were identified, including collaborative practice, co-management, and multidisciplinary team approaches. While some of these models of care describe similar concepts, others have several meanings and many do not describe an actual interaction between the nurse practitioner and physician. Outcome variables across the studies focus on patient-level, NP-level, MD-level, and organizational-level factors.