Demand for Protected Area (PA) tourism continues to grow, raising concerns for its environmental sustainability. Numerous sustainable tourism guidelines and best practice examples exist for separate aspects of PA regulation and management. However, such efforts are insufficient to reliably and holistically understand how regulation can mediate the relationship between tourism development and PA environmental sustainability. This paper proposes a theory development project, to map the compatibility and interplays among various regulatory approaches, and their consequences for sustainable PA tourism. The project is initiated here by taking the first steps toward a concession-related theory of regulation. The focus on concessions has been chosen because concessions are the most under-researched aspects of PA tourism regulation. Four regulatory aspects are selected and conceptualized in this paper: the approaches to PA planning, the types of monitoring undertaken, the methods of concession allocation and the design of environmental requirements in concession contracts. Methodologically, grounded theory is used, with data collection relying on written sources. The paper develops two sets of narrative statements regarding the prospects for PA environmental sustainability, under particular examples of concession-related regulation. The conclusion articulates several research questions, as an immediate research agenda, and calls for an international research group to be formed. Keywords: concessions, regulation, environmental sustainability, Protected Areas.