Propagation characteristics of impact-generated tsunamis are different from most tsunami originating from other sources in that both nonlinearity and dispersion remain important for a long time after generation. This is particularly true for bolides with diameters that are comparable to, or larger than, the ocean depth. Submarine earthquakes and mass gravity flows on the other hand generally produce waves with amplitudes of only a few meters. Such tsunamis are linear during generation as well as propagation, while nonlinear effects become significant only close to the shore. Tsunamis of yet other origins, such as airborne slides, huge rock falls, or exploding/collapsing volcanoes, may locally display features reminiscent to impact tsunamis, but the far-field propagation is again linear. Oceanic impacts of asteroids and comets, however, may produce huge waves in mid ocean that stay strongly nonlinear during propagation over hundreds and thousands of km.