Histone methylation is a biochemical process that involves the addition of methyl groups to histone proteins, which are key components of chromatin in the cell nucleus. This modification can occur on specific amino acids within the histones, primarily lysine and arginine. Methylation can influence how tightly or loosely DNA is wrapped around histones, affecting gene accessibility and expression. The effects of histone methylation are complex and can lead to either activation or repression of genes, depending on the specific context and location of the methylation marks. This process plays a crucial role in regulating various cellular functions, including cell differentiation, development, and responses to environmental signals.