This chapter reflects on the ways we have come to understand and indeed construct migrant background youth as a unit of inquiry within the fields of youth sociology and migration studies, with a particular focus on Australia. It provides an account of key modes of theorising young people's experiences that have developed in Australian and international scholarship over time through these different approaches and with these particular politics in mind. The chapter then outlines contemporary approaches that bring together youth studies and migration studies in order to better understand youth in 'new times'. It demonstrates how approaches to researching young people of migrant background respond to, and also shape, a changing policy environment, shifting demographic conditions and trends in theory. The chapter outlines emergent directions in theories of migrant youth identity, belonging and citizenship in light of globalisation, hyperdiversity and heightened mobility.