This chapter reviews research on migrant selection, i.e. how those who migrate differ from people who stay in their country. After discussing the different ways in which migrant selection has been conceptualized in the social sciences, I show that it has proved hard to measure empirically because it requires data on migrants and stayers in the origin country. After significant measurement progress made in the past two decades, researchers now have the appropriate tools to describe migrant selection. Results show that migrants tend to be positively selected in terms of education, other socioeconomic characteristics, health and personality traits. Yet, the level of selection varies depending on the origin, the destination and the dimension considered, but also between individual migrants from the same origin country. Finally, scholars have also documented the positive consequences of migrant selection on their health, occupational status and their children’s educational attainment.