Precision measurements with $b$ quarks and anomalies.

Precision measurements in weak decays of heavy flavoured $b-hadrons$ are highly sensitive to beyond-the-Standard-Model physics. In particular, flavour-changing neutralcurrent (FCNC) processes, mediated by $b\rightarrow s\ell\ell$ transitions, forbidden at the lowest perturbative order in the Standard Model (SM), might receive comparatively large corrections from new particles in SM extensions. Such corrections may affect different observables related to FCNC decays, such as branching fractions or angular distributions. $b\rightarrow s\ell\ell$ transitions can also be used as a sensitive test of Lepton Flavour Universality (LFU), a symmetry of the Standard Model implying that the coupling of the electroweak gauge bosons to leptons is flavour universal. Extensions of the SM do not necessarily preserve this symmetry and may give sizable contributions to the decay amplitudes. Several anomalies have been observed in FCNC processes, some of which have disappeared while others are still present and might hint to new physics. Recent results from the LHCb experiment on LFU tests in rare $b\rightarrow s\ell\ell$ decays are discussed, along with the status of $b-flavour$ anomalies.