Abstract: A fundamental change in the strategy for mammalian development amongst vertebrates has accompanied genomic imprinting linked to placental viviparity, and with epigenetic asymmetry and functional differences between parental genomes. The imprinting cycle has been incorporated into the mammalian germline cycle to allow epigenetic resetting with the erasure and re-establishment of imprints for totipotency. The emergence of the eutherian blastocyst with a distinct cluster of inner pluripotent cells is one of the hallmarks of mammalian evolution, with high regulative capacity. The imprints are protected during epigenetic programming accompanying preimplantation development for pluripotency and the derivation of iPSCs from somatic cells. Parental genomes have different roles in embryonic-extraembryonic development, but also for other tissues during embryogenesis; they may similarly be implicated in regulating mammalian physiology, behaviour, and metabolism.  Loss of imprinting underlies several human diseases.