Mainland Southeast Asia is surrounded by Middle Pleistocene archaeology in India, South China and Indonesia, but has surprisingly little to show for itself. A survey of dispersed reports on evidence of hominin activity in mainland Southeast Asia shows how this region fits into the great arc of human dispersal from Africa to Australia. Hominin-mammal associations are an important indicator of hominin evolutionary change. Mainland Southeast Asia is identified as significant because it is a geographically intermediate zone between two different hominin populations, one to the north in China and one to the south in Java. Current hominin evidence from Middle Pleistocene sites in mainland Southeast Asia is used to evaluate three models of major hominin movement and migration. The first model describes the Chao Phraya River basin as the main conduit for the movement of hominins into the region. The second model holds that hominins moved into the region from China via east Vietnam. The third model has hominins approaching the region from the west, along the coast of South Asia and Myanmar. Current evidence does not robustly support any model and continuing testing of the models' hypotheses is required.