Abstract: An earthquake-generated tsunami results from the interaction between the solid layer (lithosphere or crust) and the liquid layer (ocean) near the surface of the Earth. This article introduces the physics of such an interaction, discussing the size, energy, and propagation of earthquake-generated tsunamis. It is pointed out that one of the most important countermeasures for the prevention and mitigation of tsunami disasters is to establish a tsunami early warning system. The present problem that there are too many false alarms should be solved based on the understanding of the inter-layer interaction near the Earth′s surface.