This thesis investigates the motivations and underpinnings of Irish immigration controls in the early twentieth century. The broader empirical and theoretical literature suggest that states develop immigration controls for particular domestic needs - the protection of the national population from the intrusion of outsiders. The thesis establishes that the controls introduced in the Irish Free State in 1935 were unusual in that they appear not to have addressed a specific need for to manage immigration to the Free State. They instead replicated other controls previously introduced in the United Kingdom, a state with rather different national circumstances, and from which the Irish Free State had seceded in 1922. The research approach developed for this study is an interdisciplinary methodology of historical sociology. Because of the necessary focus on the roles of structure and agency in the process of shaping Irish immigration controls, realist social theory is adopted as the macro-level social theory used to make historical particulars generalizable. Through a narrative case study method shaped by this methodology, the thesis examines the development of Irish immigration controls. It finds that the interaction between the particular political, economic and cultural contexts of the Irish Free State shaped the process of developing immigration controls. Nationalist politics undoubtedly played a role in their evolution, but in a very different way than suggested by the empirical theoretical literature. Immigration controls are not always about immigration.