Histone H2A and H2B are the core components of the nucleosome. H2A and H2B assemble H2A/H2B dimer, and two H2A/H2B dimers combine with H3/K4 tetramer to form histone octamer. The histone octamer is wrapped around by 146 bp DNA to assemble a nucleosome, which is the basic structural unit of chromatin in vivo. H2A.Z (also known as H2AFZ, Histone Family Member Z) is a histone H2A family member. It is highly conserved from yeast to human, with 90% of its primary sequence preserved among different species, showing only 60% homology with canonical histone H2A. H2A.Z is found in approximately 10% of mammalian nucleosomes. H2A.Z has been one of the most studied H2A variants in recent years. It plays an important role in different biological processes such as DNA replication, DNA repair, transcription regulation, cell cycle, spermatogenesis, chromosome segregation, centromere structure and maintenance of heterochromatic/euchromatic status. However, different studies reported diverse conclusions in the nucleosome stability and transcriptional regulation. The contradictory roles of H2A.Z in vivo might be explained by different combinations of H2A.Z with other epigenetic regulators, PTMs on H2A.Z and interaction with chromatin binding proteins.