A historical review of the Butcher-Oemler effect in the evolution of cluster galaxies.

The Butcher-Oemler effect is one of the important topics in the evolution of cluster galaxies. It was introduced by Butcher and Oemler in 1978 for the first time. Since then, the detailed investigations to this effect have been stimulating a lot of observational and theoretical works about the contents and evolution of galaxy clusters. In this paper the discovery of the Butcher-Oemler effect, its evidences, objections, progress in recent studies, and different theorectical interpretations are historically reviewed.