This paper examines one of the must substantial labour migration flows between countries in Asia. It is of particular significance since it predominantly involves movements which are undocumented. Based on village studies in the areas of origin, the history of the movement is traced although the bulk of attention is focused on the contemporary situation. The paper demonstrates that official labour migration from Indonesia to Malaysia has increased substantially in recent years but it is only the tip of the iceberg of all movement since undocumented migration has also increased in scale and complexity. A major element in the Indonesia-Malaysia movement is the flow from East Nusatenggara to East Malaysia which forms a distinct sub-system and is examined in the paper. It is argued the onset of the recent financial crisis has not led to a diminution of the flow due to increased pressures to migrate and segmentation of labour markets for migrant workers at the destination. The causes of the movement are summarised and the evolving characteristics of the movement analysed. Over time the movement has not only increased in scale but became more complex with more women becoming involved and migrant workers entering a wider range of occupations.