This article explores the constitutional regulation of birthright ius soli citizenship in two Latin American countries which restrict access to citizenship for the children of foreigners deemed to be passing through the countries. Access to citizenship is a significant marker of membership, setting the boundaries of inclusion and exclusion within and across States. Choosing the cases of Chile and Colombia, this article uses historical, institutional and comparative analysis in order to excavate the evolving conceptions of citizenship in those two countries, with particular reference to the concepts of the 'transient foreigner' and of 'domicile'. The case studies provide an excellent laboratory within which to examine the evolution of constitutional ideas of citizenship and 'the people'. In Colombia, the outcome of the investigation shows that there is unlikely to be significant long-term change in the citizenship regime towards a more generalised acceptance of unconditional ius soli, notwithstanding the substantial shorter-term measures taken to accommodate the children of undocumented migrants from Venezuela and to respond to international pressure. In Chile, combined with other ongoing constitutional work in the citizenship space as part of a wider reform process, there may be a slow journey towards a different constitutional future for so-called 'transient foreigners' and others excluded within the State, but this is currently stalled. Chile has, however, introduced legislation cementing a more limited concept of 'transient foreigner', linking this work on citizenship to the wider domain of migration governance.