In the Standard Model (SM) of particle physics, the muon and the tau particles are simply heavier copies of the electron, coupling with gauge bosons independently of their generation. This property is called Lepton Flavour Universality (LFU).
In models beyond the SM, LFU can be naturally violated with new physics particles that couple differently with respect to the lepton generations.
Over the last few years, several hints of LFU violation have been reported in both $b\rightarrow c$ and $b\rightarrow s$ transitions. An overview of the measurements performed by LHCb during Run 1 ($\sqrt{s}=7-8~\mathrm{TeV}$) and part of Run 2 ($\sqrt{s}= 13~\mathrm{TeV}$) is reported.