The article presents a general account of xenophobic discrimination in international law. It shows that the dominant grounds-based approach to addressing xenophobic discrimination as (i) racial discrimination and (ii) discrimination based on nationality or citizenship, fails to capture what is wrong about xenophobic discrimination. Likewise, the suggestion to address xenophobic discrimination via a dedicated ground like foreignness may also fail given the unique character of foreignness as in turn constructed by other grounds. Instead, xenophobic discrimination can be understood as a sui generis category of discrimination which is not necessarily based on a particular ground, but which leads to the particular harm of making people appear as foreigners or outsiders to the political community of a nation-state. The article thus proposes a shift away from a grounds-based to a harm-based approach to discrimination in international law.