Although over the past decades the numbers of studies investigating international student mobility and migration (ISM) increased, methodological challenges in empirical research on the topic have remained mainly unaddressed. This is particularly the case for sampling, which is a crucial but often less considered part of qualitative research designs. In this article, we identify three main challenges in qualitative sampling for research into ISM: time, space and international students' heterogeneities. In addressing those challenges, we theoretically discuss their implications and give empirical examples drawing on our research experiences. We argue for a more reflexive research procedure in studying educational mobility.