Chromatin structure plays a key role in most processes involving DNA metabolism. 
Chromatin modifications implicated in transcriptional regulation are relatively 
well characterized and are thought to be the result of a code on the histone 
proteins (histone code). This code, involving phosphorylation, ubiquitylation, 
sumoylation, acetylation and methylation, is believed to regulate chromatin 
accessibility either by disrupting chromatin contacts or by recruiting 
non-histone proteins to chromatin. Recent evidences suggest that such mechanisms 
are also involved in DNA damage detection and DNA repair. One of the most 
well-characterized modifications is caused by the formation of DNA double strand 
breaks (DSBs), resulting in phosphorylation of histone H2AX (the so-called 
gamma-H2AX) on the chromatin surrounding the DNA lesion. It is generally 
believed that histone H2AX phosphorylation is required for the concentration and 
stabilization of DNA repair proteins to the damaged chromatin. The 
phosphorylation of this histone seems to play a role in both non-homologous 
end-joining (NHEJ) and homologous recombination (HR) repair pathways. However, 
the choice of the repair pathway might depend on or induce additional 
post-translational modifications affecting other histone proteins necessary to 
the completion of the entire DNA repair process. Interestingly, even in the 
absence of DSBs, histone modifications occur. Indeed, following UV-exposure, 
histone acetylation takes place and is believed to facilitate the nucleotide 
excision repair (NER) process by promoting chromatin accessibility to the repair 
factors. This review focuses on recent data characterizing the function of 
histone modification in various repair processes and discusses if the 
combination of such modifications can be the trademark of a specific DNA repair 
pathway.