Silencing in Saccharomyces cerevisiae is a form of transcriptional repression that involves the assembly of a specialized and heritable structure of chromatin. The HML and HMR loci, which contain copies of the genes found at the yeast mating-type locus, are silenced, as are telomeres. These examples share several features which are also found in position-effect variegation in flies and X-chromosome inactivation and genomic imprinting in mammals. Silenced chromatin is confined to a few special domains of the yeast genome, and active genes inserted into these domains become silenced. Molecular and genetic evidence has suggested that the establishment of silenced chromatin requires some S phase specific function. Recent experiments indicate that the assembly and maintenance of silenced chromatin can also be influenced at other phases of the cell cycle.