  Nuclear beta decays between (J^pi,T) = (0^+,1) analog states yield the best
value for the Vud element of the Cabibbo-Kobayashi-Maskawa matrix. Current
world data establish the corrected Ft values of 14 separate superallowed
transitions to a precision of order 0.1% or better. The validity of the small
theoretical correction terms is confirmed by excellent consistency among the 14
Ft values and by recent measurements that compare pairs of mirror superallowed
transitions. With consistency established, the results now yield |Vud| =
0.97420(21). This value is consistent with the considerably less precise
results obtained from beta decays of the neutron, the pion and T=1/2 mirror
nuclei, which are hampered by experimental challenges.
