The velocity and motion of landslides, once equilibrium is lost, is necessary information for the estimation of the potential damage. The Lecture will describe concepts and modelling techniques addressing this problem. Firstly, the physical phenomena and deformation mechanisms leading to fast sliding velocities will be explored. The mechanism of thermal pressurization of pore water in the sliding surface will be described and applied to simple but common sliding geometries. Criteria to decide if rapid motion is likely to occur in practice will be given.