Histones are a family of basic proteins that provide structural support for the chromosomes. DNA winds around them to form nucleosomes, which are then wrapped into the chromatin fibers. In addition to their role in compacting genomic DNA into nuclei, histones also perform a structural function in regulating gene expression. An important feature of histone biology is their ability to acquire a large set of post-translational modifications that modulate their interaction with DNA or chromatinassociated proteins. Especially, the H3 and H4 histones, which exhibit long tails protruding from the nucleosome, which can be covalently modified at several places (Table ). These modifications have been reported to be important in gene expression profiles. Histone modifications also affect transcriptional accuracy, it is therefore conceivable that the observed loss in transcriptional precision with aging is causally related to histone modifications. The major modifications that impact them are methylation and acetylation (addition of an acetyl chemical group -COCH3). Methylation abnormalities result in enhanced cancer relapse with low survival rate. Alterations in methylation upon aging are accompanied by a loss in the acetylation level of certain histones (hypoacetylation). Animal model studies have reported that prevention of age-related hypoacetylation inhibits cognitive impairment and moderates illnesses such as Parkinson's disease, osteoporosis, and stroke. Alterations in histone methylation has been considered as another characteristic feature of aging. In cases in which histone methylation has been found to impact aging, it does so by regulating transcription, categorizing it as a major mechanism of its action. Moreover, histone methylation regulates or is regulated by additional cellular pathways that contribute to or prevent aging. Cells from aged organisms show a large-scale loss of histones, specifically a gradual loss of histone H3 trimethylation at lysines 9 and 27 (H3K9me3 and H3K27me3), which are considered as repressive marks that promote chromatin compaction. Another trend is the increase in "activating" histone marks (H3K4me2/3, H3K36me3). Some of these trends are exemplified in Table . Furthermore, it is worth noting that the role of histone methylation in aging is only starting to be appreciated.