Perennial ryegrass has become the most widely sown perennial forage grass in temperate regions due to its combination of high digestibility and tolerance of grazing. The primary objectives in breeding for agricultural use are to improve total and seasonal dry matter production over a range of fertiliser inputs, digestibility, persistency, freezing tolerance and drought or heat tolerance. Adequate seed production and resistance to a wide range of diseases and pests is also necessary. Improvements in productivity and persistency so far have been achieved mainly by hybridisation and recurrent selection using the polycross method and by the use of polyploidy. Further improvements in freezing tolerance, drought and heat tolerance and, for some localities, resistance to pests and snow moulds are required to extend the geographic range of the species. Modern cultivars show little improvement in leaf or stem digestibility but a high magnesium variety is now available. Perennial ryegrass breeding is at an early stage and prospects for further progress appear good.