Pseudo Nambu-Goldstone bosons (also known as axion-like particles) with
flavour-violating couplings to the Standard Model (SM) fermions are a
rather generic consequence of spontaneously-broken global U(1)
symmetries, e.g. if the SM fermions carry flavour non-universal charges.
A possible consequence is the occurrence of flavour-violating decays of
hadrons and leptons into light axion-like particles. These exotic
signatures are a powerful probe of such kind of scenarios. I will
discuss the phenomenological consequences at future experiments,
focusing in particular on searches for lepton flavour violation.