  This talk discusses possible new physics interpretations of recent
experimental results on the B-->K*mu+mu- decay that show a discrepancy with the
Standard Model predictions. A model independent analysis that takes into
account all the relevant observables in B-->K*mu+mu- and in related b-->s
transitions allows to identify a consistent new physics explanation of the
discrepancy. An explicit realization in the context of a Z' model is presented.
The model is based on the U(1) gauge group associated with the difference
between muon- and tau-lepton number, L_mu - L_tau.
