Epigenetic changes are defined as all meiotically and mitotically heritable changes in gene expression that are not encoded in the DNA sequence itself. The field of epigenetics is becoming increasingly prominent because it presents a key to understanding differences between growing and senescent cells, tumor and normal cells, and differentiated and aging cells, which can be exploited for treatment of multiple conditions. Interwoven mechanisms, which regulate the gene expression, like DNA methylation, histone modification, and RNA-associated silencing, are recognized as players in a system of growing complexity.