The cost of feedstock is often a major barrier to commercialization for lignocellulosic biofuels. Much of the research on biofuel and biobased chemical production has focused on the carbohydrate, lignin, and lipid components of biomass. There are numerous opportunities for the use of lower-cost feedstocks if more attention were devoted to the recovery and utilization of the protein and other N-containing components. This review compiles data from the last two decades on nonedible/nonpalatable agricultural residues, deoiled seedcakes, bioethanol and biogas residues, and food wastes, with a focus on the amounts and types of N-containing components. Given the challenges of removing N-containing compounds from biofuel intermediates postconversion, a case is made for the extraction and purification of proteins (and other N-containing compounds) from low-cost lignocellulosic biomass before conversion to fuel. The goal of such processes is to avoid difficult fuel upgrading steps while enhancing the opportunities for additional biorefinery products and sustainable nitrogen cycles.