Epigenetic regulation of gene expression is a dynamic and reversible process that establishes normal cellular phenotypes and contributes to human diseases. At the molecular level, it involves hierarchical covalent modification of DNA and proteins that package DNA, such as histones. This review discusses key protein families that mediate epigenetic signaling through histone acetylation and methylation, including histone deacetylases, protein methyltransferases, lysine demethylases, bromodomain-containing proteins, and proteins that bind to methylated histones. These families are emerging as druggable enzymes and protein-protein interaction domains. The article discusses known disease links, molecular mechanisms, and recent progress in pharmacological modulation of these proteins. Chromatin is the fiber in which DNA and genes are packaged in the nucleus. It consists of DNA wrapped around histone proteins, forming nucleosomes. Epigenetic mechanisms are responsible for integrating environmental cues at the cellular level and play a role in diseases related to diet, lifestyle, early life experience, and environmental exposure. Epigenetics is of therapeutic relevance in multiple diseases, including cancer, inflammation, metabolic disease, and neuropsychiatric disorders, as well as in regenerative medicine. The dynamic nature of epigenetics allows for the manipulation of molecular factors involved in this process to alter disease-associated epigenetic states. Several molecular mechanisms contribute to epigenetic gene regulation, including chromatin remodeling, histone variant exchange, non-coding RNA regulation, DNA methylation, and covalent histone modification. Inhibitors of DNA methylation and histone deacetylase (HDAC) are approved for clinical use in hematological malignancies, providing proof of concept for epigenetic therapies. Histone acetylation is a highly dynamic process regulated by histone acetyltransferases (HATs) and HDACs. Acetylation neutralizes the positive charge on lysine, reducing the affinity of the histone tail and enabling transcription. Histone methylation involves lysine and arginine residues, with different methylation states acting as binding sites for other proteins. These modifications contribute to the physical structure of chromatin and the recruitment of specific proteins to genomic loci. Epigenetic mechanisms are involved in various diseases, including cancer, neuropsychiatric disorders, and metabolic diseases. Epigenetic regulators such as HDACs, bromodomains, and methyl-lysine-binding domains are targets for drug development. Inhibitors of HDACs and other epigenetic enzymes have shown clinical efficacy in treating certain cancers and other diseases. Recent studies highlight the potential of targeting 'undruggable' oncogenic transcription factors by inhibiting the catalytic or chromatin-interaction activities of druggable epigenetic cofactors. Epigenetic regulation also plays a role in immune responses, inflammation, and metabolic disorders. Sirtuins, which deacetylate both histone and non-histone substrEpigenetic regulation of gene expression is a dynamic and reversible process that establishes normal cellular phenotypes and contributes to human diseases. At the molecular level, it involves hierarchical covalent modification of DNA and proteins that package DNA, such as histones. This review discusses key protein families that mediate epigenetic signaling through histone acetylation and methylation, including histone deacetylases, protein methyltransferases, lysine demethylases, bromodomain-containing proteins, and proteins that bind to methylated histones. These families are emerging as druggable enzymes and protein-protein interaction domains. The article discusses known disease links, molecular mechanisms, and recent progress in pharmacological modulation of these proteins. Chromatin is the fiber in which DNA and genes are packaged in the nucleus. It consists of DNA wrapped around histone proteins, forming nucleosomes. Epigenetic mechanisms are responsible for integrating environmental cues at the cellular level and play a role in diseases related to diet, lifestyle, early life experience, and environmental exposure. Epigenetics is of therapeutic relevance in multiple diseases, including cancer, inflammation, metabolic disease, and neuropsychiatric disorders, as well as in regenerative medicine. The dynamic nature of epigenetics allows for the manipulation of molecular factors involved in this process to alter disease-associated epigenetic states. Several molecular mechanisms contribute to epigenetic gene regulation, including chromatin remodeling, histone variant exchange, non-coding RNA regulation, DNA methylation, and covalent histone modification. Inhibitors of DNA methylation and histone deacetylase (HDAC) are approved for clinical use in hematological malignancies, providing proof of concept for epigenetic therapies. Histone acetylation is a highly dynamic process regulated by histone acetyltransferases (HATs) and HDACs. Acetylation neutralizes the positive charge on lysine, reducing the affinity of the histone tail and enabling transcription. Histone methylation involves lysine and arginine residues, with different methylation states acting as binding sites for other proteins. These modifications contribute to the physical structure of chromatin and the recruitment of specific proteins to genomic loci. Epigenetic mechanisms are involved in various diseases, including cancer, neuropsychiatric disorders, and metabolic diseases. Epigenetic regulators such as HDACs, bromodomains, and methyl-lysine-binding domains are targets for drug development. Inhibitors of HDACs and other epigenetic enzymes have shown clinical efficacy in treating certain cancers and other diseases. Recent studies highlight the potential of targeting 'undruggable' oncogenic transcription factors by inhibiting the catalytic or chromatin-interaction activities of druggable epigenetic cofactors. Epigenetic regulation also plays a role in immune responses, inflammation, and metabolic disorders. Sirtuins, which deacetylate both histone and non-histone substr