Digestibility of forage crops is one of the most important indicators of livestock performance.  Genetic improvement of digestibility, resulting in improved livestock performance, can be passed on to forage and livestock producers for little or no extra cost, beyond that required to plant an improved forage variety.  Digestibility can be improved by one of three mechanisms: decreased lignification of plant cell walls, decreased cross-linking of lignin with structural carbohydrates in plant cell walls, or altered ratio of structural to nonstructural carbohydrates.  In the latter case, the so-called “high sugar” grasses have an increased concentration of nonstructural carbohydrates and a decreased concentration of structural carbohydrates.  Development of new varieties with increased water-soluble carbohydrates (WSC) has been a major breeding objective for perennial ryegrass (Lolium perenne L.) and a minor objective for several other grasses.  Heritability of WSC is moderate to high and progress is fairly rapid, resulting in increased digestibility and improved livestock performance.  In perennial ryegrass, progress has been achieved without any negative consequences on fitness or production of the high-WSC plants and varieties, despite early reports that they might be more susceptible to some diseases.  Interest is growing among forage breeders to adapt some of these successes to other forage crops.