Copyright owned by the author(s). At present, the best value for Vud, 0.97420(21), comes from superallowed 0+ 0+ nuclear transitions, of which fourteen have now been measured with high precision. The current status of world data is presented and shown to be robust. The derived Vud value is consistent with the considerably less precise results obtained from decays of the neutron, the pion and T = 1/2 mirror nuclei. Nuclear isospin symmetry-breaking corrections appear to be well under control, having been tested by on-going experiments.
