Grasslands are one of the most important ecosystems and forms of land use in the world. They are crucial for food production and deliver ecosystem services. However, particularly when used for livestock production, they are also a significant source of pollution including the greenhouse gases methane and nitrous oxide. Energy inputs into grassland agriculture, particularly fertilisers, also contribute to greenhouse gas emissions. A considerable amount of research has focused on emissions from grasslands: how to measure them and management strategies for mitigation. Similarly, there have been a number of studies on the role of grasslands in terms of carbon sequestration. However, less work has been carried out exploring ways in which genetic improvement of grassland crops can reduce emissions and enhance carbon sequestration. Plant breeding has been successful at increasing the yield, persistency and stress tolerance of the major grasses and legumes of many grasslands in the world. These same approaches have considerable potential in altering plant traits to enhance the ecological efficiency of grassland agriculture.