A comparison is made between the importance of the following categories of processes in ion-surface and laser-surface interactions: ballistic, thermal-spike, residual-defect-induced, and electronic. It is shown that ballistic processes are important for ion sputtering, ion mixing, and ion composition change. Also, they exist with laser-pulse sputtering but are not important. The picture with thermal-spike processes is the inverse, such processes being unimportant in most ion-surface interactions, but very important indeed with laser-pulse sputtering. In the latter case one must distinguish between normal vaporization and phase explosion, both of which are fundamental. On the other hand, normal boiling may possibly be unimportant owing to the negligible density of heterogeneous nuclei formed in the bulk, approx 10~6 kg~-1. However, it is essential to note that, if nuclei can be formed at the surface, the density will be much higher. Sputtering due to subsurface heating probably does not exist. Residual defects are basic to all ion-surface interactions, but most especially to ion mixing. Here most (approx 90
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