Technical Abstract: Grasses are amongst the most important crops worldwide, and the composition of their cell walls is critical for uses as food, feed, and energy crops. Grass cell walls differ dramatically from dicot cell walls in terms of the major structural polysaccharides present, how those polysaccharides are linked together, and the abundance and importance of pectins, proteins and phenolic compounds. Recent advances, spurred by the availability of genomic resources for several plant species, include the characterization of cellulose synthase like (Csl) gene families that are unique to the grasses and the demonstration that members of one of those gene families, CslF, are responsible for making the mixed linkage glucans that are unique to the order Poales.