Polysaccharide structures determine their biophysical properties and enzymatic digestibility. Moreover, plant polysaccharide structures also influence their interactions and assembly in the cell wall, and consequently, properties such as strength of wood. The action of enzymes on biomass may be influenced not only by the structure of the polysaccharide but also the molecular architecture of the cell wall. To study the assembly and molecular architecture of the plant cell wall, working with many collaborators, our research group has studied the structure of cellulose microfibrils. We have also discovered enzymes that are important for synthesis of glucuronoxylans and glucomannans. By manipulating these biosynthetic pathways in model plants, trees and crop plants, we can investigate how the structure of the polysaccharides influences the assembly of the cell wall. Using solid state NMR we can assess the changes in molecular architecture. We can show that polysaccharide structure influences the way the polysaccharides crosslink to lignin and interact with cellulose fibrils. These findings support show that polysaccharide structure and the molecular architecture of the wall influence the binding and action of enzymes for biomass conversion.