This paper constitutes a preliminary output of the ODA-funded research programme on sustainable livelihoods being carried out by the Institutes of Development Studies and the Poverty Research Unit at the University of Sussex, in collaboration with the International Institutes for Environment and Development. This programme aims to explore the alternative routes to sustainable livelihoods pursued by rural people in contrasting agro-ecological settings in four countries: Bangladesh, Mali, Ethiopia and Zimbabwe. In relation to this aim, the overall focus is to understand how institutional arrangements determine rural people's entitlements, provide the setting within which they construct their livelihoods, and determine who gains and loses in the struggle to maintain livelihoods. It is proposed that rural people construct their livelihoods via three main strategies: agricultural intensification, livelihood diversification, and migration. This paper explores the second of these strategies using evidence from Asia and Africa.