Background: The role and contribution of advanced nurse practitioners (ANP) has been well researched and found to be of great value for improving quality patient care and enhancing patient outcomes through education and health promotion. However, the role and the contribution of the ANP to gastroenterology nursing have not been evaluated either nationally or internationally. A review to determine the role and contribution of the ANP in gastroenterology nursing will inform on the contribution of the role and whether the role makes a difference to patient outcomes and cost effectiveness of patient care. Objective: This review aims to investigate the nursing role and contribution of the advanced nurse practitioner in gastroenterology. Furthermore, improved understanding of the underlying causal mechanisms explaining how the ANP role in gastroenterology nursing works, will provide a deeper understanding of how, why, for whom and in what contexts the role and contribution of the ANP to gastroenterology nursing are most successful. Methods: A realist review will consolidate evidence on how, when why and where the ANP role in gastroenterology works or fails through identifying programme theories underlying to the role’s introduction. The following steps will be operationalised; locating existing theories, searching the literature, documenting literature selection, engaging in data extraction and synthesis and refining programme theory. As an iterative approach, review cycles will uncover explanatory and contingent theories through context-mechanism-outcome configurations (CMOCc). Due to the variation in context and mechanisms, different outcomes will be likely across different clinical settings although similar patterns may be identified. Conclusions: Due to the theory-oriented approach of realist reviews, the pragmatic consequences of the review, will lend itself to deeper understanding of how the role and contribution of the ANP in gastroenterology nursing works in practice.