Epigenetics is mostly the study of heritable changes that are not caused by changes in the DNA sequence; to a lesser extent, epigenetics also describes the study of stable, long-term alterations in the transcriptional potential of a cell that are not necessarily heritable. Epigeneics include any process that alters gene activity without changing the DNA sequence, and leads to modifications that can be transmitted to daughter cells. Many types of epigenetic processes have been identified—they include DNA methylation, alteration in the structure of histone proteins and gene regulation by small noncoding microRNAs. DNA methylation is mainly mediated by DNA-methyl transferase (DNMT), there are two known types of DNMT, namely DNMT1, which preserves preexisting pattern of methylation after cell replication, and DNMT3A/B, so-called “de novo” DNMT, which methylate previously unmethylated DNA. Histone modifications mainly include acetylation, methylation, phosphorylation, and ubiquitination. The acetylation of histones can be mediated by histone acetyltransferases (HATs) and histone deacetyltransferases (HDACs), while Histhone demethylation is performed by two classes of histone demethylases: lysine-specific demethylase (LSD) family proteins (LSD1 and LSD2) and JmjC domaincontaining histone demethylase (JHDM). Epigenetic inhibitors can also work alone or in combination with other therapeutic agents.