Mammals inherit two complete sets of chromosomes, one from the father and one from the mother, and most autosomal genes are expressed from both maternal and paternal alleles. In imprinted genes, the expression of the allele is dependent upon its parental origin. Appropriate regulation of imprinted genes is important for normal development, with several genetic diseases associated with imprinting defects. A common process for controlling gene activity is methylation. The first steps for understanding the functions of DNA methylation and its regulation in mammalian development have led us to identify common (epi)genetic mechanisms involved in the eight human congenital imprinting disorders.