Although the sequence of human genome is known, our understanding of the complicated network that takes place inside cells is far from complete. Many questions still remain unanswered with the regard to how the complex genomic information is used by human cells. For example, how does the genome work to orchestrate changes in gene expression during development and differentiation? Are all genes expressed in every cell type in all human tissues? How many genes are coding or non-coding in a particular cell? What are the functions of non-coding genes? It seems clear that many answers to these questions will be found in a field of growing interest, i.e., the study of epigenetics. Epigenetic mechanisms are modifications that occur in the genetic material that do not change the nucleotide sequence, but instead may cause conformational modifications in DNA. There are basically three epigenetic modifications; DNA methylation, histone modification and regulation by non-coding RNA. This is a summary of epigenetic regulatory mechanisms and their effects on gene transcription.