Chromatin modification refers to the process by which the structure of chromatin, the complex of DNA and proteins in the nucleus of cells, is changed in order to regulate gene expression. This can involve various modifications to the DNA, such as methylation or acetylation, as well as modifications to the histone proteins that help package the DNA. These modifications can influence how tightly the DNA is packed and therefore affect whether genes are turned on or off. Chromatin modification plays a crucial role in various biological processes, including development, differentiation, and response to environmental stimuli. Research in this area seeks to understand the mechanisms of chromatin modification and how it impacts gene expression and cellular function.