Genomic imprinting is an epigenetic phenomenon found in mammals and flowering plants that leads to differential allelic gene expression depending on their parent of origin. In plants, genomic imprinting primarily occurs in the endosperm, and it is associated with seed development. The imprinted expression is driven by the epigenetic memory programmed in each lineage of female and male germlines. Several imprinted genes have been identified based on genetic studies in maize and Arabidopsis. Recent advances in genome-wide analyses made it possible to identify multiple imprinted genes including many nuclear proteins, such as transcription factors and chromatin-related proteins in different plant species. Some of these genes are conserved in Arabidopsis, rice and maize, but many are species specific. Genome-wide analyses also clarified the regulation mechanism of imprinted genes orchestrated by DNA methylation and histone methylation marks. Additionally, genetic analyses using Arabidopsis revealed new regulatory factors of DNA demethylation and imprinting and shed light on the more precise mechanisms.