The development of renewable biofuels into a major national energy resource is a key mission of the U.S. Department of Energy (DOE) Genomic Science Program. Lignocellulosic biomass has the potential to be an abundant, renewable source material for the production of biofuels and other bioproducts, but its recalcitrance to biological hydrolysis into fermentable sugars necessitates expensive chemical and enzymatic pretreatment prior to fermentation. Biomass is composed of plant cell walls, which have a complex hierarchical microarchitecture composed of cellulose microfibrils laminated with hemicellulose, pectin, and lignin polymers. To understand both the organization and deconstruction of this complex composite material, the associations and morphology of the component polymers and the enzymes acting on them must be characterized across multiple length scales ranging from nanometers to micrometers. Of particular relevance to recalcitrance are structural, dynamic and mechanical factors limiting the contact accessibility of hydrolytic enzymes to substrates and their subsequent catalytic activities. Accessibility is determined in part by matrix surface roughness, penetrability and porosity which changes significantly under pretreatment. Catalytic activity can be influenced by enzyme inhibition and by the mechanical work needed to disengage cellulose strands, which is determined by the structure, dynamics, and hydration of the cellulosic substrate. The Oak Ridge National Laboratory (ORNL) Scientific Focus Area (SFA) Biofuels Program provides fundamental information about the structure and deconstruction of plant cell walls that is needed to drive improvements in the conversion of renewable lignocellulosic biomass to biofuels. This program integrates neutron scattering with high-performance computational simulation and analysis of the plant cell wall structure and biochemistry to understand the physicochemical processes taking place across multiple length scales during deconstruction of lignocellulosic biomass with a particular focus on pretreatment.