  Searches for lepton flavour and lepton number violation in kaon decays by the
NA48/2 and NA62 experiments at CERN are presented. A new measurement of the
helicity suppressed ratio of charged kaon leptonic decay rates
$RK=BR(Ke2)/BR(Kmu2) to sub-percent relative precision is discussed. An
improved upper limit on the lepton number violating K+- --> pi-+mu+-mu+- decay
rate is also presented.
