Cells infected by with the human cytomegalovirus (HCMV) have two potential fates once the HCMV genome enters the nucleus. In an active infection there is extensive viral gene expression, viral DNA replication and release of progeny virus. In contrast, in a latent infection the lytic transcription programme of HCMV is effectively suppressed and the cells undergo latent infection. The suppression of viral lytic gene expression observed during latency is the result from the cells inability to support robust viral immediate early (IE) gene expression; crucial genes responsible for driving the lytic cycle. The repression of IE gene expression results from specific post-translational modifications of histones associated with the viral major immediate early promoter (MIEP). The histone modifications present on the MIEP impart a repressive chromatin structure preventing transcriptional activity.