This paper examines the relationship between the law and the creation of Iraq’s national territory and citizenry in the context of British Mandate rule in Iraq between 1920 and 1932. Specifically, I examine the possibility for, and scope of, a relationship between the mandate-era Tribal Criminal & Civil Disputes Regulation (TCCDR) and the process of delimiting, or “bordering,” Iraq, and defining its citizens. This is important because the population that this law specifically targeted – persons identified as “tribal” – were the overwhelming majority of people living in the highly sensitive and evolving borderlands between Iraq and Mandate Syria, Trans-Jordan, and the kingdom of Ibn Saud. The developing field of Iraqi border formation rightly examines the diffuse security, commercial, and political factors involved in the process of boundary making after WWI, but is yet to directly implicate the very law that shaped governance over those most impacted by those new borders. In this study, I will argue that the TCCDR was a factor in the origins and development of Iraq’s boundaries formed under British rule between 1920 and 1932. In addition to a thicker and more cohesive picture of boundary making in Iraq and the region, and a series of new evidence about the lived effects of Iraq’s notorious dualistic legal system, this paper’s most significant contribution is to the growing body of research that shows the borders of Mandate-era Iraq, like most other states, were not arbitrary or pre-determined, but deeply embedded in their political, social, and historical contexts. To do this, I ask: What impact did the TCCDR have on processes of early Anglo-Iraqi territorialization and boundary making, and vice versa, and how did this tribal law code inform AND reflect ideas of Iraqi-ness and citizenship at the physical (largely rural) margins of the new state? To answer these questions, I employ the theoretical frame of legal impact – how laws influence society in intended and unintended ways – at the level of communal (tribal) relations to the nascent Iraqi state and its constituent institutions and legitimizing discourses of authority. In addition to the TCCDR, my sources are the Iraqi Nationality Law of 1924, the reports of Iraqi and British administrative and intelligence officers working in the provinces, and petitions and other sources by impacted tribal leaders.