The book describes searches for charged lepton flavour violation (LFV) in the process t ¿ µ µ µ . The study is performed using the LHCb experiment data sample corresponding to the full data sample of proton-proton collisions at a centre-of-mass energy of 7 TeV (8 TeV), collected in 2011 (2012), respectively. No significantly statistical signal of the decay in question has been found and as a result, the upper limit was set. The limit was then interpreted in terms of an effective field theory approach including operators with different lepton chirality structures, taking into account effects beyond the Standard Model.Finally a combination of all LFV t decays is computed using CLs method.