Abstract Large collected dataset by the LHCb experiment, combined with unconventional ideas, allows more and more rare decays mediated by flavour-changing neutral current (FCNC) transitions, possible only at the loop level in the Standard Model of particle physics, to be put under scrutiny. In this seminar we report on the observation of a decay with b->s gamma transition, test FCNC in the up-quark sector, and use FCNC transitions to look for signs of lepton flavour violation. Finally, by studying the very rare QED process J/psi -> 4mu, we demonstrate that LHCb is in an ideal position to observe new fully leptonic B decays in the near future.

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