Perennial ryegrass shows considerable genetic variation for water-soluble-carbohydrate (WSC) content (Humphreys, 1989; Turner et al., 2002). This grass is currently widely used for livestock production in temperate agriculture as the WSC can provide the energy needed for efficient utilisation of forage protein during rumen fermentation. In the future grasses with high carbohydrate content may also be important for use in the production of bioenergy. Variation in the WSC content of ryegrass has been further characterised by quantitative trait locus (QTL) mapping. Several regions of the genome with basic control over carbohydrate metabolism were identified. To benefit future breeding programmes this increased understanding of the genetic control of sugar metabolism must be applied to develop markers that can be used for selection. Candidate genes which might explain these QTL have not been identified (Turner et al., 2006). Therefore the most appropriate way to proceed at present is with random markers from within the genomic regions of interest.