The etiopathogenesis of mood disorders is not fully understood. Among different possible causes, the involvement of genetic factors is taken into account. The manifestation of clinical symptoms cannot be assigned to a single gene mutation, thus the epigenetic association in the origin of those illnesses is suggested. The epigenetic regulation of gene expression, evoked by environmental stimuli rests upon producing persistent changes in its expression. There are several epigenetic mechanisms that change the accessibility of DNA to transcriptional factors such as acetylation/deacetylation and methylation/demethylation of the histones or an introduction of methyl groups to the cytosine of the DNA. Early and adult stress exposure is believed to have an association with epigenetic alteration of genes involved in mood regulation, for example, genes involved in the regulation of the HPA axis activity (NR3C1) or responsible for the serotonergic neurotransmission (SLC6A4). The data coming from epigenetic research indicate that mechanism of action of some antidepressants such as fluoxetine and escitalopram or mood stabilizers such as valproicacid, is at least partly associated with the epigenetic processes. Moreover, the epigenetic changes in some genes are believed to be promising diagnostic tools. These changes may help to identify the groups of patients particularly vulnerable to mental disorders and may have potential utility as biomarkers facilitating diagnosis and treatment of psychiatric disorders. Taken together, the epigenetic research will reveal neurobiological underpinnings of affective disorders and may open a new pharmacological avenue for patients suffering from mood disorders and other mental disorders.