  The impact of rare lepton decays ($\mu \to e \gamma$, $\tau \to \mu \gamma$,
>...) and rare $B$ and $K$ decays ($B\to \ell^+\ell^-$, $B\to \ell\nu$, $K\to
\pi \nu\nu$, $K\to\ell\nu$, ...) in probing the existence of an underlying
flavour symmetry is reviewd. Particualar emphasis is deveoted to the
connections between quark and lepton flavour strucutres, in the context of
generic effective field theory approach to physics beyond the SM.
