W F Vinen suggested in 1961 that the creation of quantized vortex line in superfluid He-4 is impeded by an energy barrier. Measurements of the rate nu at which negative ions nucleate vortices in isotopically pure He-4 have vindicated this idea. Barrier heights derived from the measured temperature dependence of nu are in good agreement with values calculated by Muirhead, Vinen and Donnelly (MVD) on the assumption that the nascent vortex first appears as a small loop at the equator of the moving ion. The MVD model can in addition provide a satisfactory explanation for the extraordinary sensitivity of nu to tiny traces of He-3 observed in experiments. A prediction that vortices can also be created by a fast adiabatic expansion of liquid 4He through the lambda (superfluid) transition—perhaps modelling the creation of cosmic strings at a cosmological phase transition in the early universe—has been tested. The results imply line densities that are smaller by a factor of at least 100 than those predicted. It is pointed out that Vinen’s contributions to the understanding of superfluidity have been substantial and that their influence is likely to be felt far into the future