The experimental status of generation number violating muon and kaon decays is reviewed. We concentrate on three experiments with a large PSI contribution, neutrinoless muon-electron conversion, muonium-antimuonium conversion and the decay K+ --> pi+mu(e). The SINDRUM II experiment at PSI searches for the coherent conversion of a muon into an electron in titanium. The design and construction of the SINDRUM II detector and the results of the first data-taking period in 89 are presented. In total 3.2 million events have been analyzed and no candidate for the process mu-Ti --> e-Ti has been found. Using two independent determinations of the total number of muon stops an upper limit of B(mue) <4.4 x 10(-12) (90% C.L.) is obtained. The plans to lower the sensitivity by two orders of magnitude are discussed. A muonium-antimuonium conversion experiment is being set up at PSI using the refurbished SINDRUM I detector. The goal of the experiment is to improve the sensitivity for the effective coupling constant G(MMBAR) by a factor of approximately 100. Finally a new proposal E865 has been accepted at BNL to improve the sensitivity for the branching ratio of the decay K+ --> pi+mue by a factor 70 to 3 x 10(-12).