The last years have brought profound insights into molecular mechanisms and application of epigenetics to medicine. Alteration of epigenetic profile is considered to be influential in both the normal and disease state of an organism. Various diseases, such as cancers, neuropsychiatric disease and other non-neoplastic disease are often associated with epigenetic alteration. In the light of increasing knowledge on the involvement of epigenetic factors in disease, it is now becoming apparent that epigenetic factors could be ideal therapeutic targets. In the context of the new insights of epigenetics, this review summarized the epigenetic mechanism of gene expression and the most important epigenetic pathologies.