  The concept of lepton flavour universality (LFU), according to which the
three lepton families are equivalent except for their masses, is a cornerstone
prediction of the Standard Model (SM). LFU can be violated in models beyond the
SM by new physics particles that couple preferentially to certain generations
of leptons. In the last few years, hints of LFU violation have been observed in
both tree-level $b\to c\ell\nu$ and loop-level $b\to s\ell\ell$ transitions.
These measurements, combined with the tensions observed in angular observables
and branching fractions of rare semileptonic $b$ decays, point to a coherent
pattern of anomalies that could soon turn into the first observation of physics
beyond the SM. These proceedings review the anomalies seen by the LHC
experiments and the $B$ factories, and give an outlook for the near future.
