The grass/clover ley plays a central role in most organic farms, since clover is the foundation stone for the whole farm system through its ability to fix atmospheric nitrogen. As well as providing an essential forage resource for farm livestock, grass/clover swards also form the basis of sustainable organic arable rotations. The author discusses making the most of clover and soil nitrogen mineralization, the role of herbs and the efficient recycling of manures. He also covers reducing weed invasion, clean grazing systems for worm control, efficient grazing and conservation, and minimizing the environmental impact of grassland.