Rare Kaon Decays

Historically important in the development of the Standard Model (SM) of particle physics, rare kaon decays are still a privileged tool for looking beyond it. The main reasons to continue the study of rare kaon decays are to test the CKM quark-mixing and CP-violation paradigm, to make quantitative comparisons with the B sector, and to search for explicit violations of the SM. Current research on rare kaon decays focuses mostly on decays, which are predicted with good accuracy within the SM and beyond. Experimentally, these decays, especially that of the charged kaon, have a long history. Their theoretical importance is matched only by their experimental difficulty. This article reviews the progress of the past 10 years, describes the state of the art, and looks toward future perspectives.