Epigenetics is the study of heritable changes in gene expression that occur without a change in DNA sequence. Much of today’s epigenetic research focuses on the study of covalent and noncovalent modifications of DNA and histone proteins and the mechanisms by which such modifications influence overall chromatin structure. Recently, it has become evident that RNA, particularly noncoding RNAs, also play a role in controlling multiple epigenetic phenomena. Many important aspects of plant development are regulated by changes in gene expression that derive from modifications of chromatin structure. Histone modification is an important molecular mechanism of epigenetics. In particular, the reversible acetylation and deacetylation of specific lysine residues on core histones of chromatins regulate the accessibility of chromatins and gene activity. We have shown that reversible acetylation of core histones is involved in hormonal signaling and responses to biotic and abiotic stimuli in Arabidopsis. Given the importance of histone modification in the regulation of gene expression in plants, a better understanding of how histone modification modulates gene expression may provide a new insight into how plants response to the environment during plant development.