The concept of the migration system, first popularized in the 1970s, has remained a staple component of any review of migration theory. Since then, it has been cast somewhat adrift from its conceptual moorings; today in the literature migration systems are generally either conflated with migrant networks or elevated to the heights of macro-level abstraction which divorces them from any empirical basis. At the same time, by taking on board more sophisticated notions of agency, emergence, and social mechanisms, the broader concept of the social system has moved on from the rather discredited structural−functionalist marina where it was first launched. In recent years, having been rejected by many social theorists, the social system has been subject to major reconstruction prior to its relaunch as a respectable and valuable area of social enquiry. This article argues that, for the most part, these developments in systems theory have been ignored by those applying the concept of systems to the analysis of migration. It addresses the question of how the concept of the migration system can be reformulated in the light of these theoretical advances and what implications this may have for our research and analysis.