In the Standard Model of particle physics the three charged leptons are identicalcopies of each other, apart from mass differences, and the electroweak coupling of the gaugebosons to leptons is independent of the lepton flavour. This prediction is called lepton flavouruniversality (LFU) and is well tested. In tree level decays, any violation of LFU would be a clearsign of physics beyond the Standard Model. Experimental tests of LFU in semileptonic decaysofb-hadrons or rarebdecays are highly sensitive to New Physics particles which preferentiallycouple to the 2nd and 3rd generations of leptons. Recent results from LHCb on lepton flavouruniversality inb→c`νtransitions and rareb→s``decays are discussed. The results are basedon 3 fb−1of proton-proton collisions collected at centre of mass energies√s= 7 TeV and 8 TeV.