Diversifying the teaching population is of international concern. Ireland has experienced significant socio-demographic change in the last decades, but we lack adequate data on the backgrounds of student teachers, especially in relation to nationality and ethnicity. In this paper, we examine the nationality/ies, ethnicity/ies and experiences with diversity of Ireland's 2014 undergraduate primary and postgraduate post-primary initial teacher education (ITE) applicants, entrants and non-entrants, part of the focus of the Diversity in Initial Teacher Education in Ireland national research project. The overwhelming majority of respondents claim Irish only nationality, and are of "White Irish" ethnicity. Respondents' constructions of their ethnicity privilege nationality and skin colour. The exclusionary constructions of ethnicity of those self-identifying as "White Irish" reveal the heavy influence of Ireland's post-colonial nationhood. A significant proportion reported having little or no experience with groups different to their own. We end by noting implications on policy, research and ITE programme levels.