'Mind the Gap!': bridging the theoretical divide between internal and international migration

The interdisciplinary field of migration studies is split into internal and international migration, characterised by different literatures, concepts, methods and policy agendas. Most migration scholars nowadays research international migration, even though, quantitatively, internal migration is more important. Yet the distinction between internal and international moves becomes increasingly blurred, not only because of geopolitical events and the changing nature and configuration of borders, but also because migrants' journeys are becoming increasingly multiple, complex and fragmented. We present a schematic model that sets out 10 migration pathways that combine internal and international migration, and return migration, in various sequenced relationships. We survey the limited literature that attempts to compare and integrate internal and international migration within the same theoretical framework, both general models and some case-study literature from Mexico. We consider three approaches where theoretical transfer seems to hold potential: systems approaches, migrant integration, and the migration-development nexus. We conclude that considerable potential exists for integrating the study of internal and international migration, at both the theoretical and the empirical level. Too often one is studied without reference to the other, yielding a partial analysis. However, we baulk at attempting any 'grand theory' of migration which incorporates all types of migration, in all places and at all times.