AbstractUsing 1.0fb−1 of LHCb data, searches for the rare decays B(s)0→μ+μ−, B(s)0→μ+μ−μ+μ− and τ−→μ+μ−μ− are presented. A search for D0→μ+μ− using 0.9fb−1 of LHCb data is also discussed. In the absence of an excess of events, upper limits are set on each decay mode. Both the angular analysis of B0→K⁎0μ+μ− and a measurement of the isospin asymmetries in B→K(⁎)μ+μ− are made with 1.0fb−1 of LHCb data. The measured angular and isospin observables are presented as a function of the invariant mass of the muon pairs.