I review rare kaon decays. I introduce the flavor problem and possible solutions. Very rare kaon decays like K → πνν ̄ are very important to this purpose: we study also K → πl+l−, K → ππee where chiral dynamics is important to disentangle short distance effects. We discuss also the decays K0 → μ+μ−, which have received recently some attention due to the measurement by LHCB.