  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.
