Rare decays are processes that are suppressed in the Standard Model but can happen via loop diagrams. These decays are very sensitive to new physics as particles beyond the SM can enter the loops at the same level as SM ones. This talk presents the theoretical framework to calculate b→sl+l- amplitudes and a selection of measurements from the LHCb experiment. Among these measurements particular attention is given to two analysis performed by the Birmingham group. The first is the measurement of the branching fraction of the rare Λb→Λ0μ+μ- decay, where evidence for signal at low dimuon masses is found for the first time. An angular analysis of these decays is also performed. Secondly, rare decays are used to test lepton universality, measuring the RK*0 ratio between B0 mesons decaying into a K*0 and a pair of muons or electrons.