In recent years, the covalent modification of histone tails has emerged as a crucial step in controlling the transcription of eukaryotic genes. Phosphorylation of the serine 10 residue of the N-terminal tail of histone H3 is crucial for chromosome condensation and cell-cycle progression during mitosis and meiosis. In addition, this modification is important during interphase because it enables the transcription of an increasing number of genes that are activated as a consequence of a variety of cell-signaling events. The location of the serine 10 residue in close proximity to other modifiable amino acids in the histone H3 tail enables the possibility of an interaction between phosphorylation of serine 10 and methylation and/or acetylation of lysine 9 and lysine 14. Finally, the finding that the histone H3.3 variant, which has a conserved N-terminal tail, can replace histone H3 at sites of active transcription, adds a new layer of complexity and possibilities to the regulation of transcription through changes in chromatin structure.