Constraints on new physics from rare (semi-)leptonic B decays

The measurements of rare leptonic and semi-leptonic B decays performed at the LHC, not showing any significant deviations from the Standard Model expectations, put strong constraints on new physics. A brief account of the impact of recent measurements is given. As a concrete example, models with partial compositeness are discussed, where tree-level flavour-changing Z couplings lead to potentially visibile effects in rare B (and K) decays that will be scrutinized experimentally in the near future.