The non-conservation of lepton flavour number has only been observed so far in neutrino oscillations. The observation of this phenomena in the charged lepton sector would provide clean evidence of new dynamics beyond the Standard Model.
I plan to discuss the physics of lepton flavour violating tau decays in semileptonic modes with particular attention on the determination of the relevant hadronic matrix elements. I plan to illustrate the role of these decay channels in constraining new physics scenarios by considering few specific examples. In particular, I will consider the possibility that the observed Higgs boson has flavour violating couplings to leptons.