d- cussed by Tanya Panchenko and Ben Black in Chap. 1 of this book, centromere activation or inactivation might be caused by modifications of chromatin. Such acquired chromatin epigenetic modifications are then inherited from one cell di- sion to the next. Concerning centromere-specific chromatin modification, it is now evident that all centromeres contain a centromere specific histone H3 variant, CenH3, which replaces histone H3 in centromeric nucleosomes and provides a structural basis that epigenetically defines centromere and differentiates it from the surrounding chromatin. Recent insights into the CenH3 presented in this chapter add important mechanistic understanding of how centromere identity is initially established and subsequently maintained in every cell cycle.