During animal development, their cells and tissues undergoing various forms of gene expression. Gene expression in animals is regulated by methylating their genomic DNA. After fertilization occurs the fall in DNA methylation pattern, processes by which this happens are called active and passive demethylation. New methylation of DNA molecules perform enzymes called DNA methyltransferases (Dnmt's). DNA methyltransferases can be divided into three protein families, and their role is to perform de novo methylation and maintenance of the existing methylation pattern that is inherited from parents. This paper work is presenting some of the fundamental roles of DNA methylation in the embryonic development of animals. DNA methylation participates in processes such as embryo preimplantacion reprogramming, reprogramming of the primordial germ cells, methylation based regulation of transcription, genomic imprinting and inactivation one of the two x chromosomes. Proper regulation of this processes by DNA methylation contributes to the healthy development of the embryo, while irregularities in some of these processes may contribute to the development of tumors or irregularities in the animal nervous system.