Velocities have many uses. They are used in processing as well as interpretation. In processing they allow, for example, Normal Moveout (NMO) corrections to offset arrivals which facilitates stacking of events. This increases the signal-to-noise ratio significantly and makes interpretation easier. In processing the correct velocity-depth model allows “true-to-nature” imaging of the subsurface. But especially in interpretation there are huge benefits in obtaining accurate velocities for the different “geo-bodies”, as they can be used for lithology and pore fill determination. In some processing methods, take Full Waveform Inversion (FWI), they can be the main aim of its application. It is fair to say that for an accurate image of the subsurface, an accurate velocity-depth model is paramount in obtaining a “true” image of the subsurface, in terms of structure/geometry as well as amplitudes of reflections needed for quantitative interpretation. Different velocities are in use: Wave Velocity, Particle Velocity, Interval Velocity, Average Velocity, Stacking Velocity, NMO Velocity, DMO Velocity, Migration Velocity, Phase Velocity, Group Velocity, Instantaneous Velocity, Love wave Velocities, Rayleigh wave Velocities and maybe many more. Each of these velocities are derived either by a special method or serve a specific purpose. Also, the accuracy varies. It is important to aim for the appropriate velocity, that means a velocity of sufficient accuracy for the purpose. In the course various velocity determination methods will be discussed and it will become clear that for increasing accuracy not only more advanced processing methods are needed, but also more sophisticated acquisition. Think of multi-azimuth acquisition to derive azimuth-dependent velocities providing information on fractures and in situ stresses.