CLASH-VLT is a VLT/VIMOS Large Programme carrying out a spectroscopic campaign on 13 massive galaxy clusters at a median redshift of 0.4. Upon completion, it will provide spectra and redshifts for ~7000 cluster members. I describe some preliminary results from this programme, concentrating on two topics: 1) the internal dynamics of galaxy clusters and 2) the mass function of cluster member galaxies. In 1) I present results on the cluster mass profiles, the orbits of galaxies inside clusters, and the pseudo-phase-space density profile, to set constraints on the mechanisms of formation and evolution of clusters and of cluster galaxies and on the nature of the dark matter. In 2) I investigate the environmental dependence of the mass function, to set constraints on the evolution of cluster galaxies and the formation of the intra-cluster light.