Histone deacetylases (HDACs) are enzymes that play a key role in epigenetic regulation by removing acetyl groups from histone proteins, leading to chromatin condensation and transcriptional repression of target genes; they also modify non-histone proteins, influencing processes like transcription factor activity, cell cycle progression, differentiation, apoptosis, and stress responses, with their dysregulation linked to diseases such as cancer and neurodegenerative disorders, making them important therapeutic targets.