Earthquakes are overwhelmingly dominant as a source mechanism for tsunamis, whether directly — by producing a rapid change in the seafloor topography that is communicated directly to the water — or indirectly — by triggering another event such as a landslide that in turn generates a water wave. In this presentation I shall be concerned with the coupling to water waves of rock motions that are associated with events other than earthquakes. To be specific, I refer to sub-aerial and sub-marine landslides, volcanic eruptions (pyroclastic flows and caldera collapses), and asteroid impacts. This chapter deals with the generation process only, not with propagation or run-up. I focus precisely on the process by which the kinetic energy of large-scale rock motion is transformed into the kinetic energy of water waves. Further, what are the conditions for the production of a long-wavelength tsunami as opposed to other sorts of water waves?