This paper highlights the importance of South-South migration and remittances and sets out some working hypotheses on the determinants and socio-economic implications of South-South migration drawing on a survey of the literature. The authors estimate that 74 million, or nearly half, of the migrants from developing countries reside in other developing countries. Estimates of South-South remittances range from 10 to 29 percent of developing countries’ remittance receipts in 2005. The impact of South-South migration on the income of migrants and natives is smaller than for South-North migration. However, even small increases in income can have substantial welfare implications for the poor. The costs of South-South remittances are even higher than those of North-South remittances, because of lack of competition in the remittance market, a lack of financial development in general, and high foreign exchange commissions at both ends of the transactions.