Perennial plants, growing in mixtures, make up most of the world's natural terrestrial biomes. In contrast, monocultures of annual crops are sown on more than two-thirds of global cropland. Grain and oilseed crops are the foundation of the human diet, but to date there are no perennial species that produce adequate grain harvests. Yet perennial plant communities store more carbon, maintain better soil and water quality, and manage nutrients more conservatively than do annual plant communities, and they have greater biomass and resource management capacity. These advantages provide a base from which to begin hybridization and selection for increased resource allocation to developing seeds, a decades-long process that must overcome or circumvent genetic complications. Breeding programs aimed at developing perennial grain crops have been initiated in wheat, sorghum, sunflower, intermediate wheatgrass, and other species.