Chromatin is the organized complex of DNA and protein found in the nucleus, primarily composed of DNA wrapped around histone proteins to form nucleosomes. This structure not only compacts the long DNA molecules into a manageable form but also plays a key role in regulating gene expression. Chromatin exists in two major forms: euchromatin, which is loosely packed and associated with actively transcribed genes, and heterochromatin, which is densely packed and generally transcriptionally inactive. Chromatin remodeling refers to the dynamic modification of the chromatin architecture by various enzymes and complexes, which can alter the accessibility of the DNA to transcription factors and other regulatory proteins. Modifications such as acetylation, methylation, and phosphorylation of histone proteins, as well as ATP-dependent remodeling complexes, can either enhance or repress gene expression. By controlling the physical state of chromatin, cells can regulate which genes are turned on or off in response to developmental cues or environmental stimuli, thereby influencing cell function, differentiation, and overall organismal phenotype.