In 2004, by constitutional referendum, Ireland revoked the automatic right to citizenship by territorial birth (jus soli). This event is of great significance in Europe, where consequently there is no longer a single nation that grants unrestricted territorial birthright citizenship to people born within its borders, and also represents a trend toward the revocation of jus soli within nations governed by the common law tradition. But the Irish Citizenship Referendum also invites comparative analysis with the United States, where jus soli is protected by the Fourteenth Amendment, due both to the historical and contemporary links between the two nations and the presence of contemporary pressures to undermine jus soli in the United States that are similar to those that resulted in the Irish Citizenship Referendum. In this article, we discuss both the importance of U.S. practice for the normative discussions surrounding the removal of jus soli as an automatic qualification for citizenship in Ireland, and the importance of the Irish debates as an example for the historical and normative investigation of the foundations of citizenship in the United States, especially in the field of American studies. In particular, we propose that the Irish Citizenship Referendum illuminates the need to reconsider the relationship between restrictionism in immigration and in citizenship, often cast in American Studies as a direct relationship. The Irish case shows that a successful campaign for limits on access to citizenship was made in the absence of policies limiting immigration. One of the purposes and effects of citizenship restriction in a context of increased immigration, we propose, is the creation of a dual and unequal workforce. For this reason, we argue that the elimination of jus soli as a basis for citizenship was unjustified in the Irish case, despite the popular pressures on Irish politicians, and that the pressure being placed on U.S. politicians to undermine jus soli should be consciously resisted.