This chapter develops mobility-based categories for studying young people with and without a migration background. Most migrant youth research uses the categories of ethnicity or generation. These categories hide the mobility that young people engage in such as migration but also study abroad, vacations, gap years and family visits; both for those youth who have migration in their biographies and those who do not. In a globalising world the ability of young people to be geographically mobile is increasingly a marker of difference and therefore needs to be considered when studying young people’s lives. The chapter argues that mobility-based categories shed new light on young people’s lives in three ways. First, they allow investigating elements of commonality and difference between youth, irrespective of where they or their parents come from. Second, they take young people’s past and present mobilities into account, allowing a temporal understanding of how mobility affects their current and future lives. Third, they operationalize mobility as a process rather than a one-time move. The article exemplifies mobility-based categories through a recent, large-N, primary data collection project on secondary-school student’s mobility in three European and one African country.