Abstract: HIR/HIRA, one of the histone chaperones, encoded by Hir/Hira (histone regulation) genes, were initially identified in yeast as negative regulators of histone gene expression. It has been confirmed that HIRA contains a conserved family of proteins found in various species including low eukaryotes, invertebrates and vertebrates. It is essential for proper development. Mutations of Hir/Hira genes result in very serious defects in normal development not only in yeast but also in advanced eukaryotes. Combined with the work in our group, the roles of Hir/Hira genes in the development in different species are reviewed, and the recent advances concerning the mechanisms of HIRA functioning are also summarized in an attempt to promote the research further on the exact roles of hira genes in development of eukaryotes and on their deeply operating mechanisms.