Developments in rare kaon decay physics

We review the current status of the field of rare kaon decays. The study of rare kaon decays has played a key role in the development of the standard model, and the field continues to have significant impact. The two areas of greatest import are the search for physics beyond the standard model and the determination of fundamental standard-model parameters. Due to the exquisite sensitivity of rare kaon decay experiments, searches for new physics can probe very high mass scales. Studies of the K --> pi nu<(<nu>)over bar>modes in particular, where the first event has recently been seen, will permit tests of the standard-model picture of quark mixing and CP violation.