  In this talk I discuss the role of heavy quarks in new physics searches with
tau leptons. I focus on new physics effects associated to the scalar sector
which are naturally enhanced for the heaviest fermions due to the large
hierarchy of the fermion masses. I will discuss two topics within this context:
lepton flavour violation in the $\tau - \ell$ ($\ell=e,\mu$) sector and
violations of lepton universality in tauonic $B$ decays.
