Tomographic imaging reveals seismic anomalies beneath the Sunda island are, Indonesia, that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers. The Sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the Mesozoic Tethys Ocean, In accord with previous studies, the lithospheric slab was imaged as a continuous feature from the surface to the lower mantle below Java, with a local deflection where the slab continues into the lower mantle. The deep slab seems to be detached from the upper mantle slab beneath Sumatra. This complex slab structure is related to the Tertiary evolution of southeastern Asia and the Indian Ocean region.