Non-mendelian inheritance refers to the group of phenomena and observations related to the inheritance ofgenetic information that cannot be merely explained by Mendel’s laws of inheritance. Phenomenon includingGenomic imprinting, X-chromosome Inactivation, Paramutations are some of the best studied examples ofnon-mendelian inheritance. Genomic imprinting is a process that reversibly marks one of the two homologousloci, chromosome or chromosomal sets during development, resulting in functional non-equivalence of geneexpression. Genomic imprinting is known to occur in a few insect species, plants, and placental mammals.Over the years, studies on imprinted genes have contributed immensely to highlighting the role of epigeneticmodifications and the epigenetic circuitry during gene expression and development. In this review, we discussthe phenomenon of genomic imprinting in mammals and the role it plays especially during fetoplacentalgrowth and early development.