Histone modification is a process where chemical changes occur on histone proteins, which are responsible for packaging DNA into chromatin. These modifications can include acetylation, methylation, phosphorylation, ubiquitination, and many others. Histone modifications can alter the structure of chromatin and ultimately affect gene expression, as they can either promote or inhibit the binding of transcription factors and other regulatory proteins to DNA. Research in this area aims to understand how histone modifications regulate gene expression, cell differentiation, development, and disease processes.