Forage legumes are essential for sustainable production systems, but their positive environmental and economic effects cannot be realized unless they also show persistence and yield stability. These are complex traits which depend on the interaction of different biotic and abiotic environmental factors with the genetic background of the sown species/cultivar. This chapter surveys the global cultivation of forage legumes and considers important challenges to achieving persistence and yield stability. The chapter includes a case study on the improvement of persistence in red clover by recurrent selection for general adaptation to the environment, and then discusses physiological studies on drought stress tolerance in white clover and broad-leafed birdsfoot trefoil (Lotus corniculatus L.). Finally, the chapter considers potential trends in future research into improving the persistence and yield stability of forage legumes, in the face of increasing biotic and abiotic stresses.